A rapid and convenient method for estimating S-phase cells in a population was developed which detects bromodeoxyuridine (BrdU) incorporation into DNA by means of monoclonal anti-BrdU antibodies. This immunofluorescence technique (RPMB technique) was compared to autoradiographic (ARG) detection of tritiated thymidine (3HTdr) grains incorporated into the DNA. Using incubation periods for BrdU and 3HTdr ranging from one minute to one hour and detecting their incorporation by ARG and RPMB techniques, it became apparent that the RPMB technique was far more sensitive than ARG in addition to being extremely easy to perform. Some possible utilities of the RPMB technique are discussed.

The reliability of DNA histogram analysis in accurately estimating S-phase cells from human tumors was tested by comparing the results to those of simultaneously obtained tritiated thymidine labeling index (LI) studies. Patients with chronic myelocytic leukemia (CML) during chronic phase were selected for study because the Philadelphia chromosome (Ph) was the only cytogenetic abnormality in each case and, since it is a balanced translocation, the frequently encountered problem of aneuploidy in human neoplastic cells was avoided. Unfortunately, when 30 CML patients were studied simultaneously by DNA histogram analysis and LI studies, the correlation coefficient between the two results was only r = 0.611. A comparison of three different mathematical programs for DNA histogram analysis showed that none was completely satisfactory. We conclude that DNA histogram analysis does not provide the same data as autoradiographically processed labeling index studies even in patients with Ph-positive CML during the chronic phase when the situation is not complicated by additional aneuploidy.Key terms: DNA histograms, labeling indices, chronic myelocytic leukemia, S-phase cells, histogram analysis Flow cytometry has been proposed as a rapid method for estimating the percentage of S-phase cells in a population (6). One potentially serious difficulty with this method results from the fact that it depends upon analysis of DNA histograms in which the S-phase cells are overlapped by Go + GI cells on one side and G2 + M cells on the other, making the precise quantification of the percentage of S-phase cells difficult (3). In addition, when human tumor cells are being studied, the histograms may be distorted by the presence of cells arrested in S-phase or aneuploidy, both of which further complicate their analysis (25).How useful, then, are DNA histograms in accurately estimating the percentage of S-phase cells in tumor cells obtained directly from patients? In this paper, we attempt to answer this question by comparing the results of DNA histogram analysis to those of simultaneously obtained tritiated thymidine labeling index (LD studies in patients with chronic myelocytic leukemia (CML) during the chronic phase of their illness. We selected this group of patients because the only demonstrated cytogenetic abnormality in each case was the presence of the Philadelphia chromosome (Ph), which is a balanced translocation from chromosome 22 to chromosome 9 without any loss or gain of genetic material. Hence, since this patient population was cytogenetically homogeneous, thereby obviating possible analytic difficulties that can arise from the presence of significant numbers of aneuploid cells, we were able to determine the accuracy of flow cytometric estimation of the percentage of S-phase cells in a population.In the studies described here we employed P388 mu-

SummaryRed cell carbonic anhydrase (Ca) types were investigated in 750 animals from three zebu, two exotic and three crossbred breeds. A Ca isozyme of slower mobility than the S isozyme was observed in four Sahiwal animals. The gene frequency of CaS, which was the predominant allele in all the breeds investigated ranged from 0.88 to 1.0.