The incidence and RNA electropherotypes of rotavirus in stools or rectal swabs of children with diarrhea were studied for three rotavirus seasons (1981 through 1984) in Philadelphia, Pa. We used a simplified RNA analysis method involving polyacrylamide gel electrophoresis followed by silver staining. Phosphate-buffered saline suspensions of the stools and swab eluates were examined directly by polyacrylamide gel electrophoresis-silver staining analysis and enzyme-linked immunoadsorbent assay (Rotazyme; Abbott Laboratories); electron microscopy was performed on solid stool specimens. The RNA analysis results were compared with electron microscopy and enzyme-linked immunosorbent assay results and exhibited a sensitivity and specificity greater than or equal to that of electron microscopy or the enzyme-linked immunosorbent assay. Ten different electropherotypes were detected among the 68 rotavirus RNA-positive specimens examined over the 3-year study. The predominant electropherotype was different in each season. Our results indicate that the polyacrylamide gel electrophoresis-silver nitrate strain RNA analysis of simple unextracted stool suspensions is a uniquely useful diagnostic technique; it rapidly provides both a definitive positive result and immediate determination of the RNA electropherotype, which is of value for epidemiological study.