A rapid CAMP test for the presumptive identification of Streptococcus agalactiae (Lancefield group B) is described. Sheep erythrocytes, sensitized by staphylococcal beta-lysin and suspended in phosphate-buffered saline, were used to determine the lytic capacity of the neutralized supernatant fluids of 4-h broth cultures of streptococci being tested. A total of 96.2% of 130 group B streptococci gave positive CAMP tests, that is, lysis of the sheep erythrocytes after 10 min of exposure of streptococcal supernatants, whereas none of 381 non-group B streptococci tested produced any lysis. The test described provides presumptive identification of group B streptococci within 4 h and eliminates problems of intermediate reactions so that a positive test is indicative only of CAMP factor production.