Interleukin-1 beta (IL-1 beta) mRNA-expressing cells in human gingival crevicular washings (GCW) obtained from patients with periodontitis and healthy controls were examined by in situ hybridization. GCW was done at 15 diseased sites [Gingival Index > 1; pocket depth > or = 5 mm] from five patients with adult periodontitis and eight clinically periodontal healthy sites from three volunteers GI < or = 1; PD < or = 3 mm), and then the samples were cytocentrifuged. In situ hybridization using digoxigenin-labelled oligonucleotide probe complementary to human IL-1 beta mRNA showed IL-1 transcripts in both polymorphonuclear leucocytes and mononuclear cells but not in epithelial cells in all GCW samples from diseased and healthy sites. Polymorphs were the predominant leucocytes in diseased and healthy sites, averaging 91.7 +/- 4.6 and 77.0 +/- 10.3%, respectively. The percentages of IL-1 beta mRNA-positive polymorphonuclear leucocytes in GCW samples from diseased and healthy sites were 92.3 +/- 4.7 and 80.9 +/- 10.3%, respectively. The IL-1 beta gene signals in individual cells were quantified in five samples (two healthy and three diseased sites). The mean amounts of IL-1 beta mRNA expression in polymorphonuclear leucocytes was higher than that of mononuclear cells in all samples and there was heterogeneity within the populations of polymorphonuclear and mononuclears cells in their ability to express the IL-1 beta gene. These findings indicate that IL-1 beta may be predominantly produced by polymorphonuclear leucocytes in the gingival crevice of patients with adult periodontitis and periodontally healthy controls.