Six different monoclonal antibodies directed against prostaglandin E2 were obtained from hybrid myelomas, following fusion of mouse NS-1 myeloma cells with spleen cells from a rat immunized with bovine serum albumin conjugates of prostaglandin E2. Four of them were of the IgG2a subclass and the other two were an IgG2b and an IgG2c. Affinities of antibodies for prostaglandin E2 were in the range 5.8 X 10(6)-6.7 X 10(8) M-1. Cross-reactivity experiments showed that one monoclonal antibody was directed almost exclusively against the prostaglandin E structure. The specific monoclonal antibody purified from ascites fluid was used for enzyme immunoassay, and as little as 30 pg of prostaglandin E1 and 100 pg of prostaglandin E2 were detected, which values are comparable to those obtained by radioimmunoassay. These results reveal that the hybridization technique is a reliable way to obtain prostaglandin E-specific antibody and that monoclonal antibodies can be valuable reagents for immunoassays.