The usefulness of clinical and laboratory findings for prediction of the presence of Group A streptococci on throat culture and of an increase in antistreptococcal antibodies was investigated in 693 adult patients. Several findings were shown to increase the likelihood of streptococcal isolation, alone and in combination: tonsillar exudate, tonsillar enlargement, tender anterior cervical adenopathy, myalgias, and a positive throat culture in the preceding year. Compared with a frequency of 9.7% in all patients, the probabilities of a positive culture were quite different (ranging from 2 to 53%) in subgroups of patients with different combinations of these clinical findings. The results of a leukocyte count and measurement of C-reactive protein added little additional predictive information. While clinical findings can never predict perfectly the results of a throat culture, they nevertheless can provide useful information — particularly in tending to “rule out” streptococcal infection — in adult patients with pharyngitis.