Drowsiness is a commonly experienced phenomenon following food ingestion. The present two experiments were designed to assess separately the effects of a solid meal compared to a liquid meal and to an equal volume of water, and the effects of meal constituents (high-fat, high-carbohydrate, or mixed meal) on objective postprandial sleep latencies. Ten normal male subjects participated in each study. Both studies used identical protocols, differing only in the meals the subjects were fed. All subjects underwent a pre-meal baseline nap at 1600 hours. At 1700 hours, subjects consumed a test meal. Naps followed at 1730, 1800, 1900, and 2000 hours. Sleep onset latency was determined by standard polysomnographic measures. In both studies, a one-way repeated-measures ANOVA procedure revealed no significant difference in sleep latencies among the meal conditions for the nap at 1600 hours. However, for the postprandial naps at 1730, 1800, and 2000 hours, the solid meal demonstrated a significant decrease in postprandial sleep latency compared with an equivalent volume of water (control). No significant differences in sleep latency were found between the food constituents. Results indicate that in contrast to a liquid meal, a solid meal produces a decrease in sleep onset latency when compared to an equivalent volume of water. Further, it was demonstrated that meal constituents have no effect on postprandial sleepiness.