A new sensitive HPLC method for the determination of urinary delta-aminolevulinic acid (ALA-U) was used to evaluate the relationship between blood-lead (Pb-B) and ALA-U levels in male workers exposed to lead. The differences between the ALA-U levels determined by this method (ALA-U-HP) and by a colorimetric method (ALA-U-CL) are discussed. The HPLC method gave values similar to the ALA-U-CL values at high ALA-U level. However, at low blood-lead levels (58 +/- 22 micrograms/l, n = 23), the mean ALA-U-HP level corrected by urinary creatinine level was one-third of the corrected ALA-U-CL level (0.83 +/- 0.14 and 2.4 +/- 0.5 mg/g creatinine, respectively). A significant increase of the mean corrected ALA-U-HP level was observed at 162 +/- 22 micrograms/l Pb-B (P less than 0.05, n = 26), while that of ALA-U-CL was observed at 245 +/- 30 micrograms/l Pb-B (P less than 0.01, n = 37). The regression equation based on the logistic model fitted well to the relationship data between the Pb-B level and the percentage of the subjects with corrected ALA-U-HP above the cut-off point (1.12 mg/g creatinine) and the expected Pb-B level for 50% response was 270 micrograms/l Pb-B, while it did not fit well to the relationship data between Pb-B level and the percentage of the subjects with corrected ALA-U-CL above the cut-off point (3.5 mg/g creatinine).(ABSTRACT TRUNCATED AT 250 WORDS)