Nicotinic acid has been suggested to decrease plasma volume loss after thermal injury. However, conflicting data have recently appeared, in reports of laboratory measurements of major derangements in cardiovascular function after large third-degree thermal injury. We investigated the microvascular effect of nicotinic acid on water and albumin leakage after a small second-degree thermal burn in the rat. No effect of nicotinic acid on albumin leakage was observed at ½ hour, 3 hours, or 6 hours; a minimal but significant (P < 0.05) decrease in water content of burned tissue was observed ½ hour postinjury. Our studies confirm in rats previous work with sheep and dogs demonstrating that nicotinic acid has slight, if any, effect on fluid and protein loss after thermal injury.