As part of an investigation of the developmental effects and structure-activity relationships of aliphatic acids, 2-methylhexanoic acid was administered by gavage to Sprague-Dawley rats on gestation days 6-15 at doses of 0, 300, and 400 mg/kg/day. The dams were allowed to deliver and their litters were examined through postnatal day 6. Pups that were found dead were examined for soft-tissue alterations. On day 6, two survivors per litter were preserved for skeletal examination. Maternal toxicity was demonstrated at both 300 and 400 mg/kg by weight loss and altered respiration (rales, dyspnea). In spite of the maternal toxicity present, there were no clear toxic effects on development; litter size, pre- and postnatal viability, and pup weights were unaffected by treatment. Skeletal examinations of selected pups yielded inconclusive data; a slight increase in the incidence of lumbar ribs was present a 400 mg/kg, but was not clearly attributable to treatment.