Intraperitoneal (i.p.) exposure to propanil (3,4-dichloropropionanilide) has previously been shown to affect macrophage cytotoxicity. In this study, we compared the immunotoxic effects of propanil, after different routes of in vivo administration, on cytokine production by thioglycollate-elicited peritoneal macrophages. C57B1/6 mice were treated with either vehicle or 200 mg/kg propanil i.p., or with vehicle, 40, or 400 mg/kg propanil orally. Three or 7 days later, ex vivo production of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) by macrophages after lipopolysaccharide (LPS) stimulation was determined. Both oral and i.p. propanil exposure resulted in up to a 60-70% reduction in IL-6 and TNF-alpha production by the LPS-stimulated macrophages, depending on the route, postexposure time, and dose of propanil administered. Oral exposure to propanil also caused splenomegaly and thymic atrophy in animals in much the same manner as animals exposed via the i.p. route. In vitro exposure to propanil also significantly reduced macrophage cytokine production. Thioglycollate-elicited macrophages from normal mice were cultured in the continuous presence of 0, 10, or 20 microM propanil plus LPS. This exposure caused a significant reduction in IL-6 and TNF protein production by these macrophages in a concentration-dependent manner. Northern blot analysis demonstrated that the message levels of these cytokines were reduced by approximately the same percentage as the protein levels in propanil-treated macrophages, indicating a possible transcriptional or pretranscriptional target(s) for propanil.