KAT-50, an established human thyrocyte cell line, expresses constitutively high levels of prostaglandin endoperoxide H synthase-2 (PGHS-2), the inflammatory cyclooxygenase. Here, we examine primary human thyrocytes. We find that they, too, express PGHS-2 mRNA and protein under control culture conditions. A substantial fraction of the basal prostaglandin E₂(PGE₂) produced by these cells can be inhibited by SC-58125 (5 μM), a PGHS-2-selective inhibitor. Interleukin (IL)-1β (10 ng/ml) induces PGHS-2 expression and PGE₂production in primary thyrocytes. The induction of PGHS-2 and PGE₂synthesis by IL-1β could be blocked by glucocorticoid treatment. Unlike KAT-50, most of the culture strains also express PGHS-1 protein. Our observations suggest that both cyclooxygenase isoforms may have functional roles in primary human thyroid epithelial cells, and PGHS-2 might predominate under basal and cytokine-activated culture conditions.