Triethyltin (TET), the most toxic of the alkyltin compounds is used industrially as both a catalyst and a biocide (NIOSH, 1976). Stoner et al. (1955) determined the acute toxicity of a series of alkyltins and reported that in the rat, the LD50 for TET was 5.7 mg/kg. Barnes and Stoner (1958) reported that this toxicity was independent of the route of administration. Within 30 min. of exposure to 10 mg/kg, animals exhibited generalized weakness, especially in the hindlimbs. In more severe cases, this condition progressed to both hindlimb and forelimb paralysis. Magee et al. (1957) reported that TET produced a striking interstital edema in the white matter of both the brain and spinal cord characterized by split myelin sheaths which were dilated and filled with fluid (spongy degeneration). The spongy degeneration produced by TET is similar to that observed in rats with hexachlorophene intoxication (Cammer et al., 1975) and has been reported in monkeys and cats (Hedges and Zaren, 1969). This effect is reversible after termination of exposure (Magee et al., 1957) and also occurs in peripheral nerves (Graham and Gonatas, 1973). TET-induced brain edema is associated with a reduction in total myelin content of the brain although the chemical composition of the myelin is normal (Eto et al., 1971). No change in the blood-brain barrier to trypan blue has been found (Aleu et al., 1963).