Toluene potentiated the toxic effect of acetylsalicylic acid in rats, increasing both maternal and embryonic toxicity. Minor anomalies and malformations were also altered by toluene pretreatment. At high toluene concentrations (3600 milligrams per cubic meter) the salicylic acid level in the material and embryonic plasma and in the amniotic fluid was increased above the expected concentration. Increasing aspirin embryotoxicity caused by toluene was warded off by glycine administration. -- AATA