We compared the changes of c-myc expression, cell growth kinetics, ability to reduce NBT and 3H -TdR incorporation rate of HL-60 cells in low concentration of FCS, or treated by TNF or no treatment, respectively. The results showed that, although the prolifcrative suppression of HL-60 cells treated by 50U/ml TNF was mimicked by adding 1. 0%and 0. 5%FCS in culture media, the differentiation had notappeared and it had not effected on c - myc expression, either. TNF (50U/ml) could inhibit proliferation of HL-60 cells during inducing differentiation and the expression of c-myc oncogene decreased remarkedly. The results indicated that decreased expression of c-myc in TNF treated HL-60 cells were mainly connected with differentiate maturation but not with proliferative suppression.