Immunosuppressive acidic protein in malignant diseases. Clinical relevance? The immunosuppressive acidic protein (IAP) has been described as a tumor associated marker in some solid tumors and hematologic diseases. To define the clinical relevance the authors determined the serum IAP levels in 194 patients with malignancies before initiation of therapy, 14 patients with idiopathic thrombocytopenic purpura (ITP), 28 patients with bacterial pneumonia, and 23 healthy volunteers. Immunosuppressive acidic protein was measured by radial immunodiffusion. The mean value of our controls was 405 +/- 48 micrograms/ml. This is consistent with published data. The mean values for patients with malignancies varied from 554 micrograms/ml to 698 micrograms/ml. These are only marginally higher than those observed for the controls. In contrast patients with bacterial pneumonia demonstrated significantly elevated values (1038 +/- 261 micrograms/ml). The authors conclude that IAP cannot be used as a diagnostic marker for the malignant diseases examined in this study. 