Sleep disturbance is associated with inflammation and related disorders including cardiovascular disease, arthritis, and diabetes mellitus. Given sex differences in the prevalence of inflammatory disorders with stronger associations in females, this study was undertaken to test the effects of sleep loss on cellular mechanisms that contribute to proinflammatory cytokine activity. In 26 healthy adults (11 females; 15 males), monocyte intracellular proinflammatory cytokine production was repeatedly assessed at 08:00, 12:00, 16:00, 20:00, and 23:00h during a baseline period and after partial sleep deprivation (awake from 23:00 to 3.00h). In the morning after a night of sleep loss, monocyte production of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) differentially changed between the two sexes. Whereas both females and males showed a marked increase in the lipopolysaccharide (LPS) - stimulated production of IL-6 and TNF-alpha in the morning immediately after PSD, production of these cytokines during the early- and late evening was increased in the females as compared to decreases in the males. Sleep loss induces a functional alteration of monocyte proinflammatory cytokine responses with females showing greater cellular immune activation as compared to changes in males. These results have implications for understanding the role of sleep disturbance in the differential risk profile for inflammatory disorders between the sexes.