Twenty-seven patients with chronic knee pain were examined prospectively using conventional radiography, radionuclide angiography, planar bone scintigraphy, and single-photon emission computed tomographic (SPECT) bone scintigraphy. When the results of subsequent arthroscopic examination of all three compartments of the knee were correlated with those of the noninvasive methods, SPECT bone scintigraphy was found to be most sensitive for evaluating the extent of osteoarthritis. Differences in detection sensitivity for articular cartilage damage and synovitis were greatest in the patellofemoral compartment. The frequency with which hyperemia was present in association with cartilage damage and synovitis indicates that osteoarthritis of the knee is capable of producing hyperemia and further implies that increased perfusion cannot be used to distinguish with confidence between osteoarthritis and septic processes involving the knee. SPECT (1.00) and planar (0.91) bone scintigraphy were highly sensitive indicators of torn menisci in a subgroup of 14 patients, each having a prearthroscopic clinical diagnosis of a torn meniscus. This result suggests that for patients with chronic knee pain and clinical suggestion of a torn meniscus, bone scintigraphy has significant potential as a high-sensitivity, prearthroscopic screening examination.