4-(1,1,3,3-Tetramethylbutyl)phenol (TMBP) was evaluated for acute toxic effects. Summary information from 3 acute oral toxicity tests in rats (2/group) fed dietary doses of 1.0, 1.26 1.58, or 2.0 g/kg led to mortality at 1.26 g/kg and above, and initial weight loss and slight retrograde degeneration of the kidney was seen in 1.58 and 2.0 mg/kg groups. No observable effects were noted at 1.0 g/kg. Summary reports of 3 eye irritation studies in rabbits indicate that 1% TMBP in propylene glycol administered to unwashed or washed eyes is slightly irritating and painful. Instillation of 10% and 100%concentrations showed increasing severity of effects, including corneal burns. Summary reports of primary skin irritation tests in rabbits indicate treatment-related irritation occurs with exposure to 1%, 10%, and 100% TMBP in 50B (not described).