Allergen extract was used to perform conjunctival provocation test on patients with Japanese cedar pollen conjunctivitis during the off-season, and histamine, tryptase and immunoreactive-leukotriene C4 (i-LTC4), which mainly consisted of LTE4, were measured in the lavage fluids. The results obtained in this study were as following. 1) After instillation of the allergen extract (1:20, w/v, 0.01 ml), histamine reached a maximal level of 4.63 +/- 1.67 ng/ml (mean +/- SE, n = 11) at 5 min. Tryptase appeared more slowly and the peak levels were reached at 5 min (116.6 +/- 49.6 ng/ml) or 10 min (119.4 +/- 63.8 ng/ml). In another set of the experiments, histamine peaked at 5 min (3.84 +/- 1.08 ng/ml, n = 7), and i-LTC4 reached peaks at 5 min (320 +/- 44.4 pg/ml) or 10 min (367 +/- 64.8 pg/ml). The amounts of these mediators decreased to base-line levels by 30 min. 2) The amounts of histamine retrieved from the lavage fluid were significantly correlated with those of tryptase (r = 0.819, p < 0.01, n = 11) and the weight ratio of tryptase to histamine was 41.2 +/- 10.0. These observations suggest that histamine was released from mast cells. 3) A significant correlation between the levels of histamine and i-LTC4 recovered from the lavage fluids was also observed (r = 0.736, p < 0.05, n = 7). 4) Compound 48/80 was instilled in the right eye (7.5 mg/ml, 0.01 ml) and the left eye was given allergen solution.(ABSTRACT TRUNCATED AT 250 WORDS)