Periodic sampling of wild brown trout (Salmo trutta) populations was carried on from 1939 to 1944 in 2 sections of Convict Creek, California, one closed and the other open to fishing. The adjacent stream sections were not stocked with hatchery fish 3 yrs. prior to or during the study. Sampling was accomplished by diverting the water and pumping the pools dry. The 2 populations were parallel in general trends although the unfished section averaged 5,438 trout per mile or 297.1 lb. of fish per acre while the fished section averaged 3,818 trout per mile or 68.7 lb. per acre. Natural reproduction contributed an average of over 2,750, 3-inch fingerlings per mile of stream each yr. Certain yrs. yielded large numbers of young while others yielded small numbers. Over-winter mortalities were found to vary greatly depending on the relative severity of winter. Survival of young trout was not a function of numbers present. The average over-winter mortality was 60%. Numbers of fish in each yearly brood decreased about 85% in the first 18 months of life.