Analgesic and antipyretic effects of dl-2[3-(2'-chlorophenoxy)phenyl] propionic acid (CPP) were studied in mice, rats and guinea-pigs. CPP produced a dose dependent inhibition of acetic acid-induced writhing syndrome. Its ED50 values 1 and 3 hr after oral administration were 47 and 31 mg/kg, respectively. CPP had a potent analgesic effect on bradykinin-induced nociceptive response in rats, and its ED50 value was 15 mg/kg 2 hr after oral administration. The analgesic activity of CPP in these experiments was less potent than that of indomethacin, but it was approximately equivalent to ibuprofen and 10 to 20 times as potent as aspirin. CPP had no analgesic effect on both the tail pinch and hot plate tests in mice, while CPP potentiated the analgesic effect of codeine on these tests. CPP had no effect on the nociceptive response induced by intradermal injection of bradykinin and/or EDTA in guinea-pigs. On the other hand, when CPP was given orally in a dose range of 1.25 to 5 mg/kg, it produced an antipyretic effect on yeast-induced fever in rats. The antipyretic activity of CPP was equivalent to ibuprofen and 10 to 15 times as potent as aspirin.