Ultraviolet (UV) radiation is a significant environmental hazard for humans and animals. Although the clinical effect of an acute UV exposure such as cutaneous inflammation, malaise, somnolence, chills, and fever have been appreciated for many years, the underlying mechanisms mediating these effects are poorly understood. Since chills and fever are the most dramatic systemic sequelae after a prolonged exposure to UV, we specifically examined the effect of whole-body UV irradiation on core body temperature and serum endogenous pyrogen activity of New Zealand White rabbits, correlating this with serum interleukin 1 (IL-1) activity and alterations of serum divalent cation levels. We found that an acute dose of UV irradiation (Westinghouse FS-40 lamps, 0.2 mJ/cm2/s X 8 h) resulted in a significant increase in the core body temperature 2 h post UV (0.8 degree C), peaking 5 h post UV (1.8 degree C), and returning to normal 24 h post UV. Likewise, the sera from the UV-irradiated rabbits had significant endogenous pyrogen activity when transferred into naive recipient animals, causing an increase in core body temperature within 45 min (0.65 +/- 0.12 degree C), decreasing over the next 2 h, and returning to normal 6 h post injection. No endotoxin contamination was detected in any serum samples. This post-UV febrile response was accompanied by a prolonged increase in serum IL-1 activity (5-10 X) and a significant alteration in serum divalent cation levels, with the rabbits becoming euthermic even as the serum IL-1 levels remained elevated. These findings provide new information concerning the pathogenesis and kinetics of these systemic effects after an acute dose of UV irradiation.