There is some evidence that intake of sea food rich in n-3 polyunsaturated fatty acids (PUFA) may protect against coronary heart disease (CHD). Thus, even very low daily amounts of n-3 PUFA below 0.5 g have been reported to reduce the incidence of CHD, although it is unknown by what mechanisms this may occur. Monocytes are of major importance in atherogenesis, and we therefore studied the effect of a daily supplement with 0.65 g of n-3 PUFA for 12 weeks on monocyte function in a randomized placebo-controlled trial of 32 healthy subjects. No effect of dietary n-3 PUFA could be demonstrated on monocyte chemotaxis, on chemiluminescence, or on formation of cytokines and leukotriene B4 from activated monocytes.