We have supplemented THP-1 cells, a human monocytic leukemia cell line, with arachidonic acid (AA), containing [3H8] AA, 1-25 microM, for up to 24 hours, and explored the time and concentration dependent patterns of incorporation in cell lipid classes and subclasses. Twenty-five microM AA consisted of deuterated AA ([2H8] AA), containing also [3H8] AA. Phospholipids (PL) were separated by HPLC with UV and radiodetection, and the fatty acids (FA) methyl esters were analyzed by GC. [2H8] AA pentafluorobenzyl-esters from individual lipid classes were obtained and analyzed by GC-MS. Incorporation of AA in cell lipids increased linearly with increasing concentrations, whereas 22:4 and 22:5 accumulated only at 25 microM AA. Up to 10 microM AA, more than 95% of the FA was incorporated in PL, whereas at 25 microM AA a significant proportion of the exogenous FA was incorporated in triglycerides (TG) and in diacyl phosphatidylcholine (PC). The time-course of AA incorporation showed that the peak was at 3 hours, with minimal incorporation in TG, in the presence of 5 microM, whereas the peak occurred at 6 hours, with about 50 percent incorporation in TG, with 25 microM. The data indicate that the range of AA concentrations and the time course of the incorporation of this FA in cell structural lipids are critical.