The protective effect of phenobarbitone and griseofulvin against signal grass (B.
decumbens) toxicity were studied in fifty-three Wiltshire x Malin (Indigenous
Malaysian) male sheep. Twenty-six animals were used in phenobarbitone experiment
and twenty-seven animals were used in griseofulvin experiment. Grazing on signal
grass significantly decreased the concentration of cytochrome P-4S0 and the activity
of drug metabolizing enzyme, viz. aminopyrine-N-demethylase, aniline-4-
hydroxylase, UDP-glucuronyltransferase and glutathione-S-transferase in liver and
kidney of sheep. The concentration of cytochrome P-4S0 was determined in
microsomal fraction according to the method of Omura and Sato (1964a) as described
by Mazel (1971). The activities of aminopyrine-N-demethylase and aniline-4-
hydroxylase were determined using Mazel, 1971 method by estimating th
