Enteric-coated tablets of aspirin-vitamin C, produced by nine Japanese makers, were examined in a disintegration test, for serum salicylate level after one oral administration and after repeated oral administration for six days.The analgesic effects of the drugs and adverse reactions to the drugs were investigated in the patients and compared with the patients' salicylate levels.As a result of these studies, which entailed administration of aspirin-vitamin C 6 T (as aspirin 1.5 g) three times a day, no significant difference could be found, between the analgesic effects of these drugs and the effect of a placebo. However, a clear difference between the drugs and the placebo was found in the adverse reactions to the drugs, at a level of significance of 5%.As for serum salicylate levels during repeated oral administration for six days, it was observed that the serum salicylate level during administration of entericcoated tablets tended to be slightly lower than that during administration of the same quantity of aspirin powder. There was no relationship between the serum salicylate level and the patients' evaluation of analgesic effects or adverse reactions.