The polyethylene glycol (PEG) antiglobulin test (AGT) was evaluated by testing antibodies in the sera of 362 different patients and by screening of 4,685 random patient sera with both the PEG AGT and the albumin AGT. Agglutination in the PEG method was stronger in 254 (70.2%), identical in 99 (27.3%) and weaker in 9 (2.5%) of the 363 sera. Mean end-point titers of the antibodies measured with the PEG method (n = 137) were 2-3 dilutions higher than with the albumin method. In sera with anti-K and anti-Fy^b antibodies the mean titer in the PEG method was only one dilution higher. Antibodies within the rhesus system were also tested with a two-stage enzyme test. Agglutination in the PEG method was stronger in 93 (50.3%), identical in 64 (34.6%) and weaker in 28 (15.1%) of the 185 sera. Mean antibody titers(n = 76) in the PEG method were 1-3 dilution steps higher for the various specificities than in the enzyme test. In 92 (2.0%)of the 4,685 sera screened in the PEG method, specific antibodies were detected; with the albumin method in 74 (1.6%)sera. The antibodies only detected with the PEG method had the specificities anti-D, -C, -C^w, -c, E, -K, -Jk^a and -M. Not detected by the PEG method were anti-Le^a antibodies in one of the sera. It is concluded that the PEG AGT is a sensitive technique for the detection and identification of red cell antibodies and that it is superior to the albumin AGT.