To investigate the production of $C_{21}$-steroids during the spawning period of spotted sea bass, Lateolabrax maculatus, we have incubated maturing and ovulating follicles with radiolabeled pregnenolone and $17alpha$-hydroxyprogesterone for 24 hours. The resulting metabolites were analyzed by thin layer chromatography (TLC) and high performance liquid chromatography (HPLC), When maturing follicles ($700sim800{mu}m$ in diameters) were incubated with radiolabeled precursors, $C_{21}$-metabolites were corticosteroids and $17alpha$-hydroxy, $20eta$-dihydroprogesterone ($17alpha20eta OHP$). When ovulation follicles ($1,000sim1,150{mu}m$ in diameters) were incubated with radiolabeled precursors, the major $C_{21}$-metabolites were $17alpha20eta OHP$, $17alpha$,$20eta$, 21-trihydroxy-4-pregnen-3-one ($17alpha20eta21P$), and corticosterone. Additional chromatography by TLC and HPLC confirmed the presence of radioactive $17alpha20eta OHP$ in the maturing follicles, and $17alpha20eta OHP$,$17alpha20eta21P$ and corticosterone in ovulating follicles. Although $17alpha20eta OHP$ was found in a small peak, the synthesis of this steroid suggests that it may play a role in regulating the oocyte maturation process. Whereas ovulation is regulated by both $17alpha20eta OHP$ and $17alpha20eta21P$ in the spotted sea bass. In addition, an unusual finding was the biosynthesis of corticosterone. Whether this production is responsible for the ovulation, and is an area requiring continued research.