The distribution of chicken (Gallus domesticus) tissue (muscle, oviduct, heart, brain, kidney, and liver) aldolase isozymes was established electrophoretically. Each tissue, being composed of varying proportions of six isozymes, has a distinct isozyme pattern. Brain, oviduct, and heart tissue possess five isozymes of aldolase: 1, 2, 3, 4, and 5. Leg and breast muscle of adults possess aldolase 5. Kidney and liver predominantly possess aldolase 6 with traces of isozymes 1–5. Aldolase 1 corresponds to aldolase C of mammals, 5 to aldolase A, and 6 to aldolase B.Antibodies to 5 react with 2, 3, and 4, but not with 1 and 6. Aldolase 5 hybridizes in vitro with 1 to form 2, 3, and 4. Aldolase 6 also hybridizes in vitro with 1 to form three intermediate hybrids, but these hybrids have not been detected in tissues. These observations imply that aldolase 1 (C) and 5 (A) are frequently synthesized simultaneously in the cell with the formation of the 2, 3, and 4 hybrids. Aldolase 6 (B), in contrast, may not be accompanied by the synthesis of other aldolases in the same cell. Pure preparations of aldolases 1, 5, and 6 were found to have similar molecular weights but different enzymatic properties.