Serum amyloid A (SAA) concentrations correlate well with C-reactive protein (CRP) concentrations. However, SAA is sometimes raised in disease when CRP is normal. This appears to occur more often in certain diseases such as rheumatoid arthritis, primary biliary cirrhosis and chronic active hepatitis. SAA concentrations did not distinguish between cancer with and without metastases as previously indicated, although mean concentrations were higher in more advanced tumours. Despite the higher sensitivity of SAA over CRP in the inflammatory response, SAA has little advantage over CRP in the assessment of malignant disease.