Although alterations in development due to inorganic lead poisoning have been intensely investigated, little is known about the early toxicity of organic lead compounds. Assessment of developmental consequences due to triethyl lead (TEL) intoxication presently included (1) determination of the acute LD50 as 13 +/- 1 mg/kg, and (2) detailed examination of early neurobehavioral sequelae. The offspring of 12 Fischer-344 dams were administered on postpartum day 5 either a sham-injection, 15% ethanol, 3 mg/kg or 6 mg/kg TEL vis SC injection (20 microliters). Small, but significant, weight reductions of 6% and 13% for the 3- and 6- mg/kg TEL-dosed pups, respectively, were observed (days 14-30). Early sensory deficits of TEL pups as indicated by impaired olfactory discrimination on day 7 and decreased incidence of nipple attachment on day 9 were accompanied by the presence of fine whole body tremor (day 10). While these initial effects were transitory in nature, activity evaluations demonstrated persistent hypoactivity in high dose TEL males (days 15, 22, 24, 26, and 29). Passive avoidance acquisition was not affected by TEL treatment (day 18). However, 72 and 144 hr tests of passive avoidance retention (days 21 and 25) suggested alterations in affective behavior, i.e., hypoactivity in high dose TEL males and hyperactivity in low dose TEL females. A reduction in number, but not magnitude, of startle responses also occurred as a function of TEL exposure. The single postnatal day 5 injection of TEL thus produced transitory effects possibly reflecting direct TEL pharmacological activity, as well as apparent long-term effects suggesting potential permanent alterations in behavioral function.