The objective of this study was to assess the effect of conjugated linoleic acid isomers (CLAs) on the expression and activity of phospholipases A(2) (PLA(2)) in human macrophages. Macrophages were incubated with 30 microM cis-9, trans-11 and trans-10, cis-12 CLAs for 48 h. After incubation, the total activity of phospholipases as well as the expression of mRNA for cytosolic (cPLA(2)) and secretory (sPLA(2)) phospholipases and activity of sPLA(2) were measured. Both CLA isomers reduced the total activity of PLA(2) (by 30.2%, P < 0.01 for cis-9, trans-11 CLA and by 30%, P < 0.001 for trans-10, cis-12 CLA). Trans-10, cis-12 CLA isomer downregulated the expression of mRNA of sPLA(2) and decreased the enzymatic activity of this enzyme (by 23%, P = 0.02) in macrophages. Conjugated linoleic acid isomers can significantly reduce the activity of PLA(2) in macrophages and downregulate sPLA(2) expression. The consequence of this effect may be reduction of releasing the arachidonic acid (AA) from the cellular membranes of macrophages.