Chemiluminescence (CL) production by phagocytosing polymorphonuclear leukocytes (PMNLs) was measured by an automatic photoluminometer with built-in mixing and temperature controls. Agitation of the vials with PMNLs and opsonized zymosan particles influenced both the lag time and the CL production. Maximal production was obtained by continuous mixing of the samples, the reaction peak occurring within 6 min. Increasing the temperature from 20 to 40 degrees C also increased the CL production, and in further experiments 37 degrees C was used. Aggregation of the PMNLs was avoided by washing the cells in PBS containing gelatin 1 g/l. Glucose, Ca2+ and Mg2+ in the final reaction mixture were necessary for maximal CL responses. The measurements of CL per s up to 4 min, the peak CL value, or the integral below the CL curve up to 6 min were all linearly proportional to the number of PMNLs in the reaction mixture. Since the lag time and the time before reaching peak CL may vary, the integral below the curve up to 6 min was chosen as the mode of CL measurement. On repeated measurements the coefficient of variation was 6.3%. The mean CL integral value for PMNLs from 14 healthy individuals was 205 +/- 19 mVs, indicating a good reproducibility of the standardized assay.