The effect of phenobarbital and phenylbutazone treatment on the renal damage induced by the toxic mushroom Cortinarius speciosissimus was studied in female rats. Phenobarbital sodium was given in drinking water (0.05% solution) for 11 days prior to the administration of mushroom. Phenylbutazone was given s.c. in doses of 50 and 100 mg/kg 1 h before the mushroom administration. Homogenized mushroom was given orally by stomach tube at a dose of 250 mg dried mushroom/kg body weight. It was found that the phenobarbital treatment strongly increased the damage induced by C. speciosissimus in the tubules of the kidney cortex but had no effect on the inflammation in the renal outer medullary zone induced by this toxic mushroom. Phenylbutazone treatment had no effect on the renal damage induced by C. speciosissimus.