Objective: This study evaluated the responses of the retinal and cutaneous microcirculation to acute hyperlipidemia and hyperhomocysteinemia. Methods: Twenty-five clinically healthy men (mean age 24±2 years) were studied four times in a randomized order, with intervals of at least one week between the two dietary interventions always preceded by a day for baseline assessment. The two interventions consisted of either 0.1g/kg l-methionine to induce hyperhomocysteinemia or of 500ml whipping cream (30% fat) to induce hyperlipidemia. Microvascular vasodilator responses to flickering-light and to cutaneous acetylcholine iontophoresis were assessed by retinal vessel analysis and laser Doppler flowmetry respectively. Results: The fat load produced significant increases in triglycerides and total cholesterol which was accompanied by a reduction of the retinal arterial flicker response. Methionine administration induced a threefold increase in homocysteine levels and a concomitant decrease in retinal venous flicker response. Acute hyperlipidemia and hyperhomocysteinemia had no effect on cutaneous microvascular vasodilator responses to acetylcholine. The inter- and intra-subject reproducibility was higher for retinal vessel analysis as compared to laser Doppler flowmetry. Conclusion: The retinal microcirculation is more sensitive to metabolic changes than the cutaneous microcirculation and can be reliably assessed by retinal vessel analysis. Reproducibility of retinal vessel analysis may be enhanced by multi-vessel assessment.