Long-term dietary omega-3 fatty acids improve coronary endothelial function in CAD patients, heart transplant recipients and diabetics. This study assessed whether short term omega-3 fatty acids affect radial artery function in CAD patients. A high resolution A-mode echotracking device (NIUS 02) was used to measure continuously, radial artery internal diameter at rest, during flow mediated vasodilation (FMD), during cold pressure test (CPT), and after sublingual glyceryl trinitrate (GTN). We studied 18 male CAD patients in a randomized, double blind, placebo controlled design. Between pre- and post-intervention measurements 24 h apart, nine subjects received 18 g fish oil concentrate (6.4 g eicosapentaenoic acid and 3.9 g docosahexaenoic acid) and nine subjects 18 g placebo. In the placebo group correlation between both baseline diameters was 0.98; P < 0.001. Pre-intervention FMD was 7.5+/-5.6%, CPT mediated vasoconstriction was 3.8+/-2.5%, and GTN induced vasodilation was 15.7+/-9.8%. Vascular responses post-intervention showed no significant difference to pre intervention, there was no significant difference between both treatment groups. The radial artery does not seem to be an immediate target for vasodilatory actions of omega-3 fatty acids.