Production of smallmouth bass (Micropterus dolomieui) of ages I through V were calculated in the Maquoketa River, Iowa, from 1978 through 1982. Total production of smallmouth bass ranged from 6.4 kg/ha during 1981 to 15.0 kg/ha in 1979; mean production for the five years was 10.1 kg/ha (S.D. = 3.53). Age III smallmouth bass contributed 41% of the total production over the five years while age II fish were second at 27%. The mean production/biomass ratio of 0.34 was found to be lower than most warm-water fish species.