Control and U-937/ptsp53 A2 cells were seeded at 200,000 cells/ml in culture medium and incubated at 37°C, 32.5°C, and 31.5°C. After 48 h, viability was assessed by trypan blue exclusion. Concomitantly, cells were subjected to cell cycle analysis by flow cytometry as described in "Materials and Methods." Mean values from three experiments are shown. Viability of control cells was always >95%, and the fraction of control cells with a sub-G1 DNA was always <10%.