Following single administration of carbon tetrachloride (p.o., 200 microliters/200 g) to female rats, activities of transaminases AST and ALT were determined from 1 hr to 7 days after the intoxication. At the same time intervals, aminopyrine breath test (ABT) was applied. The results indicate that marked decrease of ABT was observed within the first 3 hrs of exposition and lasted 24 hrs. On the other hand, statistically significant elevation of plasma enzymes was demonstrated from the 3rd hr of administration and lasted also 24 hrs. The results indicate that ABT reacts more rapidly to carbon tetrachloride administration than the changes of plasma transaminase.