 RESULTS: The TB rates cases per 100 personsyear in the three treatment groups were 3.4 in 6H, 4.5 in 3RH and 1.9 in 2RZ. The relative risk for TB with 6H as compared with 2RZ was 1.76, and with 3RH, 2.34. Twenty-seven percent of the patients voluntarily abandoned chemoprophylaxis and 9.7 were withdrawn due to adverse side-effects. Seven patients were withdraw due to hepatotoxicity 5 in 6H, 2 in 3RH and 0 in 2RZ. No appreciable differences were found among the three regimens. 