In patients with severe underlying disease and in polytraumatized patients, clinical signs of septicemia caused by infections with gram-negative bacteria are observed postoperatively with increasing frequency. Using a photometric LAL test, a longitudinal assessment of LAL reactivity on 41 intensive care patients was performed. Postoperatively, all patients developed a septicemia of different severity with body temperatures greater than 38.5 degrees C. Dividing the individual disease course, related to body temperatures, into three phases (A-C) it was found that independent of the severity of septicemia, the majority of patients (38/41) yielded a positive LAL reactivity. In phase B (body temperature greater than 38.5 degrees C) more plasma samples contained LAL-reactive material than in phase A and C (body temperature less than 38.5 degrees C). A decline of fever (phase B to C) correlated significantly (P less than 0.05) with the change from positive to negative LAL reactivity. In patients with high leukocyte counts (15-50 X 10(9)/l) a positive LAL reactivity was found more frequently. The majority of patients (21/27) who survived were transferred with negative LAL reactivity to the general wards. The results suggest that single determinations of LAL reactivity are of limited clinical validity. Using the individual profile of LAL reactivity gained through a longitudinal assessment, data upon the development of the disease course can be obtained.