1. Rats established on a normal (20% protein) diet or a protein-deficient (3% protein) diet were given either a subcutaneous injection of turpentine (5 ml/kg), which induces formation of aseptic abscesses, or saline. Plasma samples were obtained at timed intervals (0-14 days) after the injection for determination of albumin, total protein, alpha 2-macroglobulin (a major acute-phase protein in the rat) and interleukin-6 concentrations. The magnitude and pattern of the acute-phase protein response was then compared with the local inflammatory reaction, assessed histologically, and with changes in the circulating concentration of interleukin-6, which is an important mediator of the acute-phase protein response. 2. After turpentine injection there was an early fall in the plasma albumin and total protein concentrations in both normal and protein-deficient rats. After 12 h the total protein concentration increased in both groups of animals reaching a peak at about 48 h, whereas the plasma albumin concentration continued to fall reaching a minimum at 48 h. The main alpha 2-macroglobulin response was delayed and attenuated in the protein-deficient rats (onset 9 versus 24 h, peak concentration 8.95 +/- 0.5 versus 5.33 +/- 0.75 g/l, P < 0.01, and area under the concentration-time curve 18.43 +/- 2.13 versus 7.96 +/- 1.48 g/l-1 days, P < 0.01, in the normal group and protein-deficient group, respectively). 3. The circulating interleukin-6 concentration showed a transient early rise at 1 h, and was followed by a larger more sustained peak at 6-48 h.(ABSTRACT TRUNCATED AT 250 WORDS)