We measured effects of an increase in the largemouth bass minimum length limit from 254-mm to 406-mm and a decrease in the creel limit from 10 per day to 3 per day in Tradinghouse Creek Reservoir, Texas, from 1985 to 1987. Electrofishing and rotenone surveys were used to measure regulation effects on largemouth bass population and predator-prey parameters; angler surveys were used to determine effects on creel rates. After the regulation was implemented, the population structure shifted from one dominated by small, young individuals to one dominated by larger, older fish. Although relative weight among stock-quality and quality length groups declined, growth rates remained stable. Estimates of available prey remained below optimum levels. Angler catch rates increased 89%; harvest rates declined 70%.