The tissue concentrations of several inflammatory mediators were determined from day 0 to day 60 in granuloma induced in rats (n = 105) by injection of carrageenan in the fascia of the latissimus dorsi muscle. Noncollagen proteins (NCP) and the number of polymorphonuclear leukocytes (PMN) and mast cells were also assessed. In comparison with the tissue at time 0, we noted in the inflamed tissue (at 4 h) an increase in total proteins (4.0 +/- 3.0 vs. 84 +/- 12.0%, mean +/- SEM) and PMN (0.0 +/- 0.0 vs. 43.3 +/- 13.4%), and a fall in histamine concentration (from 30.0 +/- 9.0 to 9.0 +/- 4.0 ng/ml). A partial disappearance of mast cells and an increase of PAF-acether (PAF) levels (1.0 +/- 1.0 vs. 30.0 +/- 22.0 ng/ml) was noted at 16 h, whereas lysopaf remained unchanged (3.7 +/- 4.0 vs. 3.5 +/- 1.0 ng/ml). During evolution towards chronic inflammation (day 10-60), NCP decreased, PMN disappeared and mast cells reappeared; the histamine level rose to 11.0 +/- 2.0 mg/ml, thus not reaching back baseline values. Lysopaf rose to 7.1 +/- 12.2 ng/ml and PAF levels increased further to reach 240.0 +/- 153.0 ng/ml at day 10. This study suggests that PAF may contribute to the acute phase of an inflammatory state such as the carrageenan-induced granuloma and that it is also present during the chronic process.