Soluble and membrane-bound phosphatase and phosphodiesterase activities are present in preparations of 1,3-beta-D-glucan synthase from pea epicotyls. UDP-glucose phosphodiesterase and non-specific alkaline phosphatase could be partially inhibited by N-ethylmaleimide or iodoacetamide and partially removed from membranes by washing. Such treatments helped to prolong 1,3-beta-glucan synthase activity. Nevertheless, the 1,3-beta-D-glucan synthase activity in washed membranes still gradually decreased during incubation in buffer at 30 degrees C. The rate of decay was reduced by adding more specific phosphatase inhibitors, e.g. molybdate, vanadate or fluoride, or by addition of nucleotides, and much of the loss of 1,3-beta-D-glucan synthase activity during preincubation could be restored by addition of phosphatidylethanolamine to the assay mixtures. It is concluded that membrane phospholipid is an essential part of the environment of 1,3-beta-glucan synthase and must be maintained intact in order for the enzyme to remain fully active.