Two hundred and seventy-seven patients with a broad spectrum of neoplastic diseases, including 10 classes of solid tumours and three classes of haematologic malignancies, were retrospectively surveyed, and from the same sample of plasma or serum their concentrations of serum amyloid A (SAA), serum amyloid P component (SAP), C-reactive protein (CRP), and carcinoembryonic antigen (CEA) were measured. SAA levels varied from 105 ng/ml to 105,000 ng/ml, and mean SAA levels were higher in patients with metastatic tumours than in those with limited disease (P less than 0.001). Similarly, CRP levels varied from less than 8 micrograms/ml to 328 micrograms/ml and were significantly higher in the metastatic disease category. In contrast, SAP levels varied from 32 micrograms/ml to 120 micrograms/ml and showed no difference in patients with limited or metastatic disease, although an overall slight elevation was present. CEA levels were available in 150 patients and were significantly higher in patients with advanced lung or breast cancer than in patients with limited disease. The correlation between mean SAA and CRP levels was significant (r = 0.74, P less than 0.001), suggesting that SAA originates as an acute-phase protein rather than as a tumour cell product. However, the consistent elevation of SAA in all tumour types and the more marked elevation in metastatic disease may make its measurement useful in malignancy.