The effects of prostaglandin PGE2 on apoptosis and antioxidant enzyme activities were studied in two coelomocyte fractions of holothurian Eupentacta fraudatrix in vitro and in vivo. PGE2 (10(-8) - 10(-6) M) modulated apoptosis in a time- and concentration-dependent manner in both fractions studied in vitro. In vivo, PGE2 induced apoptosis at concentrations of 0.1-1 microg/g in the fraction enriched with morula-like cells. Phagocytes were more sensitive to the regulating effect of PGE2. In this fraction, PGE2 induced apoptosis at concentrations from 0.01 to 1 microg/g, while PGE2 at 10 microg/g demonstrated an antiapoptotic effect. In all experiments, apoptosis development was accompanied by a disbalance of the antioxidant enzyme system, primarily, decreased catalase activity.