The differentiation of HL-60 promyelocytic cells toward mature granulocytic cells induced by dimethyl sulfoxide (DMSO) was accompanied by a quantitative similar increase in alkaline phosphatase (ALP) activity and decrease in protein kinase C (PKC) activity. The combination of DMSO and sphinganine (SP), a potent inhibitor of PKC, increased in parallel the percentage of mature cells and the ALP activity. The enhancement of DMSO-induced differentiation and the potentiation of the decrease of PKC activity by SP also seemed to correlate with each other. Our results indicate that both ALP and PKC may play a role in the DMSO-induced granulocytic differentiation.