Two generations of selection for increased body weight in Kansas (AU-KS-2) and Marion (AU-MS-2) lines of channel catfish, Ictalurus punctatus, resulted in a 12% and 11% increase in body weight at market size, respectively. The second generation of selection produced no improvement in growth, and there was a slight negative response to selection for body weights during the second generation. Cumulative realized h2 was 0.17"0.03 and 0.15"0.03 for AU-KS-2 and AU-MS-2, respectively, based on growth performance measured against a randomly bred, Kansas control for the two generations. Relative size differences were established by the time the fish reached 80 g, and these relative size differences were maintained the remainder of the experiment. Growth rate of the channel catfish ? blue catfish /, I. furcatus, hybrid was 35% faster than the Kansas control, and better than all three groups of channel catfish. The growth improvement through interspecific hybridization was three times better than through mass selection.