The inflammatory activity and biodegradation of poly(3-hydroxybutyrate) were examined. Poly(3-hydroxybutyrate) sheet did not cause any inflammation in the chorioallantoic membrane of the developing egg. The i.v. injection of 14C-labelled poly(3-hydroxybutyrate) granules showed that 86, 2.5 and 2.4% of the total radioactivity administered were distributed in the liver, spleen and lung, respectively, and the radioactivity decreased slowly but steadily in most tissues examined during 2 month. Crude extracts of rat tissues showed that the activity degraded the poly(3-hydroxybutyrate) granules in vitro.