The hypothesis that chemically induced overt maternal toxicity induces a characteristics syndrome of adverse developmental effects in the rat was investigated. Pregnant animals (Sprague-Dawley strain) were dosed by oral gavage with one of a series of compounds on days 6-15 of gestation. These chemicals were diquat (DIQ), ethylene-bis-isothiocyanate (EBIS), toxaphene (TOX), styrene (STY), 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenol (2,4,5-Tr), triphenyl tin hydroxide (TPTH), and cacodylic acid (CAC). Significant maternal weight reductions were noted during the course of treatment with all compounds except CAC and 2,4,5-Tr. Maternal lethality was produced by EBIS, TOX, 2,4,-D, and 2,4,5-Tr. The main treatment-related developmental toxicity noted in litters at term consisted of increased lethality (EBIS, TPTH) and decreased fetal weight (EBIS and CAC). Treatment-related anomalies were seen in litters treated with 2,4-D and TOX (supernumerary ribs) and with EBIS and STY (enlarged renal pelvis). No significant developmental effects were produced with DIQ, or 2,4,5-Tr. The study indicates that overt maternal toxicity as defined by weight loss or mortality is not always associated with the same defined syndrome of adverse developmental effects in the rat.