Leukotrienes (LT) have been proposed to be important mediators in the etiology of the acute asthma attack (AAA). We therefore studied blood LT levels in 18 children having AAA. Heparinized blood samples were obtained before and after treatment with epinephrine injections and/or metaproterenol inhalations in the emergency room. The samples were acidified and subjected to Sep-pak chromatography. Reverse phase high performance liquid chromatography (RP-HPLC), ultraviolet (UV) spectroscopy and bioassay on guinea pig ileum were used to identify the LT based on comparison to data produced by standard synthetic LT samples. Radioimmunoassay (RIA) was used to further confirm the presence of LT. LT C, D and E were detected in the plasma of children having AAA. Only LT C levels were significantly elevated over control values. The mean blood LT C level of control patients was 1.6 +/- 1.2 nanograms per milliliter (ng/ml, mean +/- SEM) while that of the asthma patients was 73.8 +/- 18.2 ng/ml prior to treatment. After emergency room treatment the asthma patients had a mean blood LT C level of 22.5 +/- 11.7 ng/ml. Lowered levels of LT C accompanied improved clinical condition of the patients. This finding indicates that the AAA in children is associated with elevated blood levels of LT C.