A study of mercury accumulation in trout taken from the trout parks and streams of southern Missouri is presented. Mercury in trout is determined by digestion in nitric acid, sulfuric acid, and potassium permanganate, followed by reduction and aeration for measurement by cold vapor atomic absorption. The mercury accumulation in trout collected and analyzed in this project ranged from 0.1 to 0.3 ppm of mercury (μg of mercury/g of tissue). Previous analysis of trout collected in the mid to late 1940s from the same areas indicated mercury accumulations of approximately 3 ppm. Over the past 25 years, there appears to be a decrease in mercury found in trout of southern Missouri.