OBJECTIVE To determine the incidence of alloimmunization against red cell antigens and the thermal amplitude and specificity of antibodies in multitransfused patients and multiparous women. METHODS Antibody screening was performed in 30 nontransfused orthopedic surgery cases (control), 504 multitransfused patients and 325 multiparous women. Antibody screening at 4°C, 22°C and 37°C was carried out in a saline phase, by indirect antiglobulin technique (IAT), using papain cystein, low ionic strength solution (LISS) and polyethylene glycol (PEG). RESULTS In multitransfused patients IgM antibodies were more frequently detected at 4°C and the IgG antibody incidence was 7.1% by enzyme method, 7.7% IAT, 9.4% LISS, 10.2% using PEG & 10.2% multiparous women. Bad obstetric history cases had significantly higher incidence of alloimmunization. The antibody specificity of antibodies was mainly in Lewis, Rh, Kidd and MN systems. CONCLUSIONS Antibody screening before transfusion, at set time intervals after transfusion and during antenatal period is recommended.