Changes of PRPP-related enzyme activities and incorporation rates of glycine, Hx and Ad into acid soluble fraction (ASF) of HL60 cells were studied during terminal differentiation induced by incubation with 1.6% DMSO for 43 hours. Activities of HPRT, APRT, and PRPP synthetase were determined in homogenate treated with activated chacoal. H(A)PRT activities were measured based on the determination of conversion of 14C-labeled Hx (Ad) to IMP (AMP). PRPP synthetase activities were measured as follows; PRPP, which was formed by interaction of R-5-P, ATP and enzyme solution, was measured by HPRT assay system. Incorporation rates of Ad, Hx, and glycine into purine nucleotides were measured after incubation at 37 °C for 20 min in the presence of the respective 14C-labeled compound in HB101 medium. ASFs of cell pelletes, which were obtained by silicon oil procedure, were chromatographed. Radioactivities of all purine nucleotides were counted. HPRT and APRT activities increased 3.3 folds (4.69 to 15.70 nmol/min/106cells) and 1.5 folds (4.20 to 6.26) higher, respectively, but no increase in PRPP synthetase activities was shown. The incorporation of glycine decreased 2.2 folds (215 to 99 pmol/min/106 cells) lower in rate, but those of Ad and Hx showed no remarkable changes. It was concluded that the decreased rate of de novo synthesis was a major change during terminal differntiation.