A special cultivation technique of separated blasts of peripheral blood in suspension culture has been used for cytogenetic diagnosis of patients suffering from acute nonlymphocytic leukemia, chronic myeloid leukemia, and refractory anemia with excess of blasts. Twenty-three patients were examined; in ten cases isolation of blasts was performed on Ficoll-Verografin and in the remaining 13 patients further separation of T-lymphocyte precursors by means of sheep erythrocytes was performed. Remarkably, a 100% success rate was attained in all cultivations. The optimum harvesting time was 72-96 hours; the rate of cell division per cultivation was determined by means of bromodeoxyuridine incorporation; second mitoses were revealed only after 96-hour cultivation. In all patients, except one, abnormal karyotypic changes were ascertained in separated blasts of peripheral blood cultivations. In most cases the morphology of chromosomes obtained from separated blasts of peripheral blood cultivations was of excellent quality.