Lipopolysaccharide (LPS)-stimulated TNFalpha production is reported to be greater for whole blood (WB) cultures prepared from patients with a history of preterm birth than cultures obtained from women with a history of term birth. The objectives of this study were (1) to determine if there is a similar differential responsiveness for peripheral blood mononuclear leukocytes (PBML) and (2) to determine if treatment with aspirin influences LPS-stimulated TNFalpha production in these patients. WB and PBML were obtained from women with a history of preterm delivery before 32 weeks (cases; n=5) and age- and race-matched controls (n=5) with a history of uncomplicated term delivery. WB and PBML were cultured and stimulated with LPS. All participants then took aspirin daily for 1 week and responsiveness of PBML and WB cultures to LPS was retested. The history of preterm labor was found to have no effect on LPS-stimulated TNFalpha production in cultures of WB or PBML. Aspirin treatment enhanced LPS-stimulated TNFalpha production by PBML from controls but not cases. We conclude that endotoxin responsiveness of women with a history of preterm birth is similar to that of women with a history of term birth in terms of in vitro TNFalpha production. Aspirin increases TNFalpha production by PBML in control women but not in women with a history of preterm birth. The divergent responses to aspirin treatment in patients with and without prior preterm labor may reflect differential regulation of cytokine production by prostaglandins in women with preterm labor associated with infection or inflammation.