Decamethrin is a synthetic pyrethroid insecticide that has been under investigation by the World Health Organization for use in some vector control programs. Decamethrin proved to be a highly toxic pyrethroid ester. The acute LD50 for adult female rats was 31 mg/kg by the oral route and 4 mg/kg by the intravenous route of administration. The LD50 was observed to be sex and age dependent, with higher values recorded for weanlings and males. Initial signs of decamethrin poisoning included profuse salivation and convulsive movements. Weakness, dyspnea, anorexia and staining of the fur were observed beyond the first day following compound administration. Absorption of decamethrin was rapid by the inhalation route and minimal by the dermal route of administration. No evidence of teratogenic activity was found in rats or mice at dose levels that produced marked maternal toxicity, and no persistent toxicity was observed in neonatal rats that received perinatal exposure to decamethrin. No mutagenic activity was detected in three different in vitro assays, with or without metabolic activation.