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The number of decaying lymphocytes in the peripheral blood of the mouse was determined by means of the dye exclusion test. Under normal conditions the lymphocyte decay was very constant (1.1%). Treatment with pertussis vaccine, anti-lymphocyte serum, and hydrocortisone either alone or in combination greatly influenced the number of decaying blood lymphocytes. Treatment with heparin markedly increased the number of circulating non-viable lymphocytes, probably due to inhibition of the reticuloendothelial macrophage system. Methods for determination of the average period a decaying lymphocyte stays in blood were elaborated and used under normal and experimental conditions.

Comparative microspectropholometry of the DNA content of Feulgen-stained megakaryocytes from the bone marrow and from those retained in the pulmonary circulation showed that the ploidy classes 8 N, 16 N and 32 N are found in both bone marrow and pulmonary circulation, whereas the 64 N class is found in the bone marrow only. Electron microscopic examination of megakaryocytes retained in the lungs revealed typical ‘naked nuclei’.

Microspectrophotometric investigations of Feulgen-stained rat bone marrow megakaryocytes, comparing the traditional smear method and a new 1 G sedimentation and 40 degrees C evaporation (S. E.) method, have shown that the latter reveals a significant group of megakaryocytes (ca. 30 percent) with a DNA content of 64 N. This group is totally absent when the smear method is used.

The immunological phenotypes of leukemia cell samples from 60 patients, of whom 54 had acute myeloid leukemia (AML), were assessed with a panel of monoclonal antibodies (Mabs) with specificity for the following epitopes: Epitopes associated with myeloid leukemia cells, Epitopes expressed only on immature myeloid cells (or subsets) and on monocytes, Epitopes only expressed on granulocytes or on granulocytes and mature myeloid cells (promyelocytes, myelocytes and monocytes), Epitopes on HLA-class II (DR) and HLA-class I molecules and on insulin receptors. This panel of Mabs proved useful to identify leukemia cells in blood and to assess their myeloid origin. The panel of Mabs was found also to be useful for immunophenotyping of leukemia cells. Furthermore, the analysis revealed considerable variations in the immunological phenotype of AML cells, reflecting antigenic heterogeneity within the individual leukemia cell population as well as abnormal or no expression of histocompatibility antigens and insulin receptors in some samples. Some of the Mabs bound preferentially to subgroups in the French-American-British (FAB) classification.

Treatment of adult AKR mice with tissue-specific mitotic inhibitor mol. wt. 1,000--20,000 extracted from the AKR thymus significantly delayed the onset of spontaneous thymus leukaemia, whereas extracts of other organs were without effect. A slight prolongation of survival time was found with spleen extract when administered to BALB/c mice infected with Rauscher virus, which causes leukaemia starting in the spleen. Thymus extracts of MW 100,000--300,000 caused myocardial degeneration in some leukaemic and nonleukaemic mice.