Conflicting reports exist concerning ultraviolet-B (UVB) effects on keratinocyte (KC) interleukin-1 (IL-1) expression. To clarify the modulatory effects of UVB on IL-1, the following study was undertaken. Normal human epidermal KCs cultured in a standard low Ca2+ and serum-free medium were irradiated in quiescent phase with UVB. In this study, we used semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) to determine the mRNA level of interleukin-1 alpha (IL-1 alpha) and interleukin-1 beta (IL-1 beta). After exposure to 100 or 300 J/m2 UVB, a transient increase in mRNA levels was observed within 1 hour for IL-1 alpha and 3 to 6 h for IL-1 beta. Following this transient induction, mRNA levels for both IL-1 alpha and IL-1 beta returned to steady-state levels after 100 J/m2. After 300 J/m2 irradiation, IL-1 alpha and IL-1 beta levels were downregulated compared to unirradiated cultures at 24-h post-irradiation. The half-life for IL-1 alpha and IL-1 beta was estimated using actinomycin D treatment. Both IL-1 alpha and IL-1 beta mRNAs half-lives (t1/2) decreased faster in irradiated cells (t1/2 = 30 minutes for IL-1 alpha and 2 h for IL-1 beta) compared to unirradiated cells (t1/2 = 1 h and 4 h, respectively). These results suggest that IL-1 alpha and IL-1 beta mRNA expression are differentially regulated by UVB. In contrast to down-regulation of mRNA levels, a significant increase in IL-1 alpha protein levels, measured by ELISA, was observed in culture supernatants from 6 h to 24 h after 300 J/m2 UVB irradiation. Cycloheximide treatment did not abrogate this increase in IL-1 alpha protein level. Since this dose of UVB irradiation decreased the stability of IL-1 alpha and IL-1 beta mRNA, this suggests that the release of IL-1 alpha after UVB irradiation was due to leakage from UVB-damaged cells and not from de novo protein synthesis.