A rapid latex agglutination slide test for group A betahemolytic streptococcal throat infections was prospectively evaluated. Resident physicians, working in an adult nonacute emergency room, recorded clinical data and collected throat swabs from 729 adult patients with sore throats. Research assistants obtained throat swabs from 329 control patients. Sensitivity and specificity, compared with routine cultures, were 96% and 97%, respectively. Analyses of clinical predictions and of test results for control patients, however, suggest that this test may perform better than routine culture. The test provides a rapid, accurate, potentially useful alternative for diagnosing group A beta-hemolytic streptococcal pharyngitis in adults.