Competitive interactions between white suckersCatostomus commersoniand yellow perchPerca flavescenswere evaluated in a whole-lake manipulation experiment with one treatment lake and one reference lake. After a 2-year pretreatment period, 80% of the adult white sucker population was removed from Douglas Lake, Michigan, with trap nets set during the spring spawning season of 1987. Following white sucker removal, the abundance of chironomid larvae and the mayflyCaenissp. increased 13–18-fold in Douglas Lake, In Little Bear Lake, the control lake,Caenissp. showed a 20% decline in abundance during the study period (1985–1989), and chironomid larvae showed a 2.2-fold increase over the same time period. Associated with the increase in benthic invertebrate abundance in Douglas Lake, the diet of adult (>age-0) yellow perch shifted from predominantly zooplankton to predominantly benthos. This shift was accompanied by an increase in mean stomach content weight and feeding rate, eventually becoming apparent as increased growth. Relatively small changes in feeding rate and no trend in the diet or growth rate of adult yellow perch were apparent in the reference lake. The size structure of the adult yellow perch population in Douglas Lake showed a small increase in the proportion of large (> 150 mm total length) individuals during the first 3 years following white sucker removal and a great increase during the fourth year. In the control lake, no significant change in the population size structure of yellow perch was observed. From these results, we suggest that removal of adult white suckers can be a useful management tool to improve yellow perch growth and the quality of yellow perch fisheries. Changes in yellow perch growth and size structure, however, did not occur immediately after white sucker removal and were relatively small in magnitude during the duration of this study.