Three serological markers of immune cell activation, interleukin-2 (IL-2), soluble interleukin-2 receptor (sIL-2R), and interleukin-4 (IL-4), were measured by enzyme-linked immunosorbent assays in 20 control subjects and 26 periodontitis patients. The experimental group comprised 19 juvenile/post-juvenile and 7 severe generalized periodontitis patients with radiographic evidence of alveolar bone loss. Although some control sera contained immunoreactive IL-2 (2 of 20) and IL-4 (3 of 20), all contained sIL-2R, the levels of which correlated well with age (r = 0.644). Mean levels of all three markers were significantly elevated in the sera of patients with periodontal disease compared to control values. However, there was a wide variation in the amounts detected; IL-2 (0.21-173.33 ng/ml); sIL-2R (217.95-1177.27 units/ml); IL-4 (3.17-16.35 pg/ml), which did not correlate with either the degree of bone loss or pocket formation observed clinically. Moreover, there was no correlation between the levels of IL-2, sIL-2R or IL-4 for any given individual in the experimental group. The finding that only 2 of the control sera contained IL-2 (10%) compared to 23 of the periodontitis patients (88.5%) suggests that, of the three parameters investigated, the measurement of IL-2 could provide a sensitive laboratory test for assessing periodontal disease activity. Nevertheless, a definitive study to determine the relationship of serum IL-2 levels to clinical parameters of disease activity will be necessary to confirm this observation.(ABSTRACT TRUNCATED AT 250 WORDS)