Human bladder cancer is a common malignant tumor that may be produced by factors such as lifestyle, environment and occupation. The aim of this study was to evaluate parameters related to the viability of exfoliated urothelial cells. Exfoliated urothelial cells were obtained from 83 urine samples of 22 healthy participants (20-53 yr). From 67 of these samples, cells were transferred to collagen-coated 24-well plates. Parameters including sample volume, pH, osmolality and participant age and gender were examined on cell viability. In successive cultures, the numbers of cell colonies and cells per cell colony were determined. The number of viable cells in the urinary sediments of males varied from 0 to 6.5 x 10(3) cells per sample (mean 1 x 10(3)). Higher cell numbers in urine samples from females (6 x 10(3)) were due to considerable amounts of exfoliated vaginal cells. Cell numbers in males were positively related to volume, osmolality, and pH of the samples, as well as to the retention time of urine in the bladder. Cell proliferation was achieved in 25 out of 67 samples and was positively related to sample osmolality and pH. Participant age and content of urinary oxalates exerted negative effects on cell proliferation in vitro. The mean number of cell colonies per sample was 1.7. The mean cell number per colony was 11.7 x 10(3). It appears that high variability in individual excretion of urothelial cells able to proliferate is a limiting factor for routine use of these cells for in vitro toxicology.