This study assessed the developmental immunotoxicity of trichloroethylene (TCE) in B6C3F1 mice exposed via drinking water (0, 1,400, 14,000 ppb) from gestation day 0 (GD0) to either 3 or 8 weeks of age. Lymphocyte proliferation, NK cell activity, SRBC-specific IgM production (PFC response), splenic B220+ cells, and thymic and splenic T-cell immunophenotypes were assessed at 3 and 8 weeks of age. Delayed type hypersensitivity (DTH) and autoantibodies to ds-DNA were assessed in 8-week old animals only. Proliferation and NK cell activity were not affected at either age. Decreased PFC responses were noted in male offspring at both ages and both TCE treatment levels. PFC responses in female offspring were suppressed by treatment with 14,000 ppb TCE at both ages assessed and at 1,400 ppb TCE at 8 weeks of age. Splenic numbers of B220 cells were only decreased in 3-week old pups exposed to 14,000 ppb TCE. The most pronounced alteration in T-cell subpopulations were increases in all thymic (CD4+, CD8+, CD4+/CD8+, and CD4-/CD8-) T-cell types in 8-week old animals. DTH was increased in females at both TCE levels and in males at the high dose only. These results indicate that TCE may be an effective developmental immunotoxicant and suggests that additional studies are required to determine the health risks associated with developmental exposure to TCE.