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Intraerythrocytic parasites of Plasmodium vinckei and Plasmodium berghei were separated according to their developmental stages using discontinuous Percoll gradients. Contaminating nucleated blood cells such as leukocytes were removed by elutriation centrifugation. The stages were unequivocally identified in smears using a newly developed DNA-specific staining procedure with mithramycin and fluorescence microscopy. This stain can also be used to detect parasites in human blood of very low parasitemias. The combination of methods described has many possible applications in immunologic and biochemical parasite research.

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After aggregation of erythrocytes from malaria infected mice, the parasites (Plasmodium vinckei) could be set free using gentle mechanical forces. The mixture of freed parasites, infected and non-infected erythrocytes, and membraneous material was separated by free-flow electrophoresis. The free parasites produced were very pure and infectious. Morphological and enzymatic data on the separated fractions are presented. Free-flow electrophoresis also allowed the separation of infected and uninfected erythrocytes.

Singe-cell suspensions of gastrointestinal carcinoma and mucosa were stained with fluorescent dyes for determination of carcinoembryonic antigen (CEA) and epithelial membrane antigen (EMA). According to measurements in a Fluvo-Metricell flow cytometer and computerized data analysis the carcinomas contained between 1% and 30 % of CEA-and EMA-positive cells. In the GO/GI cell cycle phase there was a substantial antigen presence; this was rare in populations with higher degrees of chromosome set multiplication. In twothirds of the patients the mucosa was negative or only slightly stained, while in the remaining third it was stained to a moderate degree or almost as intensely as the tumor.