A cytological study was made of short term primary cultures of monkey kidney epithelial cells grown in serum-containing (M-H) and synthetic (SM-2) media. The mitotic activity of the cultures reached a peak 3 to 5 days after seeding, and rapidly declined if the medium was not changed. With replenishment at 48 hour intervals a high mitotic rate was maintained through the 8th day. Cultures subjected to a glycine- and glucose-deficient medium showed a sharp decline in mitotic activity within 24 hours. When such cultures were replenished a burst of mitotic activity occurred 20 to 30 hours later.
Mitotic aberrations such as multipolar spindles, anomalous spindles with scattered chromosomes, lagging or precocious movement of chromosomes, chromosome fragments, and chromosome bridges were found in all cultures ranging from 16 to 40 per cent of the dividing cells. Non-mitotic aberrations such as giant nuclei, multinucleate cells, nuclear fragmentation, micronuclei, nuclear inclusions, and phagocytosis were found in approximately 3 to 7 per cent of the non-dividing cell population. The frequency and types of mitotic abnormalities were generally independent of the medium used and the mitotic index of the cultures.