A study was conducted to determine the pattern of St. Louis encephalitis (SLE) virus activity in the avian populations of the Los Angeles metropolitan area in 1986. In total, 679 birds of 42 species were captured at 7 study sites. The overall prevalence of SLE neutralizing (N) antibody of 3% indicated enzootic transmission. Antibody prevalences were higher in birds sampled in the central part of the metropolitan area, which was consistent with other epidemiologic data. The use of specific avian species as sentinels for future surveillance of SLE virus activity was suggested.