Conclusion(1) The Penn-Hall seroflocculation test was not found to be a satisfactory cancer selective procedure. Although it was seldom positive in normal individuals (5% of 129), it wras positive in only 43% (96 of 241) of cancerous patients. Incidence of false positive results in 1608 non-cancerous patients was 19%. If patients with allergy, arthritis, acute tuberculosis or syphilis, temperature over 99.6°F and those with trauma, surgery or blood transfusion in prior 10 days were omitted as Penn and Hall suggested, the false positive results and the correct positive results were equally reduced by about 6%. (2) Positive results were more frequent among patients who had elevated blood sedimentation rates or who had inflammatory disease processes. As we evaluated, it is highly improbable that the reaction is cancer specific, a finding agreeing with the results of other investigators(3,4,5,6).