Biotin-binding and immunological methods were employed to demonstrate the similarity of oviduct and non-oviduct avidin in the chicken. Oviduct avidin was induced after oestrogen pretreatment by progesterone and non-oviduct avidin by intestinal tissue injury or by intraperitoneal actinomycin D administration. Avidin in the intestine, lung, bursa of Fabricius, plasma, pectoral muscle and liver after injury had biotin-binding activity similar to that of progesterone-induced oviduct avidin: (1) a temperature of 79-83 degree C was required for 50% of the maximum [14C]biotin uptake, (2) maximal exchange occurred only at 90 or 100 degree C and (3) denaturation of protein, i.e., loss of biotin-binding activity, was not yet observed at 100 degree C. Avidin in the intestine, lung, bursa of Fabricius, plasma and pectoral muscle also showed an identical cross-reaction with oviduct avidin. Furthermore, the increase in avidin-like biotin binding in the oviduct and most non-oviduct tissues was significantly correlated with the increase in avidin-like antigen in the tissue. This indicates that avidin induced in chicken non-oviduct tissues by injury or inflammation caused by actinomycin D administration is similar to progesterone-dependent oviduct avidin.