THERE have been few previous cytogenetic studies of patients with polycythaemia Vera (P.V.). Nowell and Hungerford (1962) and Nowell (1965) investigated the chromosomes of the bone marrow and peripheral blood in five patients with polycythaemia who had been treated with radio-phosphorus ("P). They found abnormal cell lines in four patients, one of whom had developed leukaemia. Kenip, stafford and Tanner (1961) examining the bone marrow by the short-term culture method, found that seven out of nine cases of polycythaemia were normal, one patient had a cell line of 48 chromosomes, and one patient (who subsequently developed frank chronic granulocytic leukaemia) showed Phl -positive cells. Both these patients had been treated with 32P. An abnormal clone having a deletion of one of the C group chromosomes was present in the bone marrow of a patient with P.V. (Solari, Sverdlick and Viola, 1962) : this patient had received X-rays and 32P. Levan, Nichols, Hall, Low, Nilsson and Nordtn (1964), using the blood leucocyte culture method, found hyperdiploid cell lines in a male patient with P.V. who had received " I ? . He had a few features of chronic granulocytic leukaemia. In all these previous studies, it is not known to what extent the chromosomal abnormalities are due to the disease or are secondary to treatment. It is clearly established that 32Pproduces typical radiation damage of the chromosomes of blood leucocytes (MacDiarmid, 1965). A few cases of P.V. have been investigated in the terminal stages of the disease, after the development of a leukaemic state (Ford, Jacobs and Lajtha, 1958: one case; Baikie, Jacobs, McBride and Tough, 1961 : two cases). In each case, short-term bone-marrow culture showed hypodiploid counts.per cu.niiii. N indicntcs ni~rinal lrvcls. Wlicrc the relative tendency to ovcr-production has altcrcd as between the t h e types of cell, this is indicatcd by giving n second asses~inent. the bulk of the aspiratc was prcpared for chromosomc analysis by a slight modification of the dircct iiicthod of Tjio and Whang (1962). Blood leucocytes were cultured for 72 hours in the prescricc of phytohaeiiiagglutiiiiii (PHA) (Difco) either by the iiiethod of Moorhead, Nowell,

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Defects of immunoregulation which occur in haemophilia, reflected by numerical changes in T lymphocyte subsets, have been further investigated in functional studies. Polyclonal T-cell activation by the mitogen phytohaemagglutinin (PHA) and specific stimulation by cytomegalovirus (CMV) or herpes simplex type 2 (HSV-2) in previously sensitized subjects were studied in peripheral blood lymphocyte and in T4-cell-enriched cultures. Compared with 12 controls, the responses of 11 patients (nine with haemophilia A and two with von Willebrand's disease) to PHA were significantly reduced both in unfractionated and in T4-cell-enriched peripheral blood lymphocyte cultures. Reduced responses to PHA were found in HIV (HTLV III)-seronegative as well as -seropositive patients. There were no significant differences between the response of patients' unfractionated and T4-enriched peripheral blood lymphocytes to CMV/HSV-2 recall antigen and the control subjects, although there was evident variation in the magnitude of patients' unfractionated and T4-enriched lymphocyte responses.

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