AbstractWe have estimated the levels of Interleukin‐1 beta (IL‐1β) by ELISA in gingival crevicular fluid (GCF) at 58 sites from 37 patients with adult periodontitis. GCF was collected for 5 s on filter papers and a 2nd sample was collected for 30 s 1 min later. 68/116 strips yielded detectable levels of IL‐1β. IL‐1β was present in both the 1 st and 2nd samples at 28 sites, in the 1 st only at 4 sites and in the 2nd only at 8 sites; 18 sites were below the level of detection for the assay. When the concentrations of IL‐1β were calculated in the original volume of GCF on each strip, the mean value for positive strips was 34.16±29.45 (SD) pg/μ1 with a range from 1.75 to 97.13 pg/μ. There were no statistically significant correlations with the plaque index, bleeding index or probeable crevice depth (pocket depth). The results indicate that IL‐1 is present in the GCF from a proportion of sites with evidence of previous perio