On the basis of early study on effects of retinoic acid (RA) on the differentiation of mouse lymphocytic leukemia-lymphoma cell strain (SACIIB 2), further research has been performed by studying the effects of retinoic acid on the human T lymphocytic leukemia cell line CCRF-CEM(CEM). The results showed that the growth of CEM cells was inhibited by RA at a concentration of 10 mumol/L. The activity of alpha-naphthyl acetate esterase (ANAE) and the percentage of CD3 positive cells rose after 10 days' RA treatment but the E rosette forming cells didn't increase. The activity of purine nucleoside phosphorylase (PNP) of the treated CEM cells increased significantly without change in activity of adenosine deaminase (ADA). The expression of terminal deoxynucleotidyl transferase (TdT) was also reduced to some degree. The analysis of lactic acid dehydrogenase (LDH) isoenzyme showed that the activity of LDH3 increased after RA treatment but without LDH1 and LDH2 expression. The results indicate that RA can induce CEM cells to differentiate.