AbstractThe activities of two phosphatases (E. C. 3.1.3.1 and 3.1.4.1) and four glycosidases (E.C. 3.2.1.21, 3.2.1.30, 3.2.1.31 and 3.2.1.51) were measured by fluorescence spectrophotometry, and flow cytometry, in mitogenstimulated lymphocytes, and in cultures of Molt‐4‐F and F‐89 cell lines, syncronized by hydroxyurea or thymidine.All enzymes were active throughout the cycle but the activities of three enzymes were elevated at specific points in the cycle, alkaline phosphatase activity increased at G2+ M/G1boundary and in early S‐phase, the activity of β‐Lfucosidase was elevated in G1and late S‐phase. Orthophosphate diesterase activity was elevated at the G1/S boundary, and during G2+ M. The increase in β‐Lfucosidase activity was due to an increased number of cells showing activity, whilst the increase in orthophosphate diesterase activity was attributable to an increase in cellular enzyme activity.Only the activities of orthophosphate diesterase and β‐Lfucosidase were measurable by flow cytometry, alkaline phosphatase activity was mainly extracellular, and therefore not detectable by flow cytometri