BACKGROUND. Antiphospholipid syndrome (APS) denotes antibody-induced thrombophilia with recurrent thrombosis and/or complications in pregnancy. One of the possible mechanisms of thrombosis in APS may be linked to diminished production of vasodilator nitric oxide (NO). It is known that reduced availability of NO leads to dysfunction of the endothelium and increased platelet aggregation. Local heating of the skin to temperatures below pain threshold (42°C) induces a biphasic increase in skin blood flow that is mediated by two independent mechanisms. The initial rapid increase is caused by a sensory axon reflex followed by a brief nadir and the secondary slowly rising plateau that is predominantly dependent on NO mechanisms. The aim of our study was to compare vasodilator response of cutaneous microvasculature to local heating in APS patients and healthy controls of the same sex and age. METHODS. In our prospective study we included 34 patients and 34 healthy controls. Subjects (48 females and 20 males) were divided into three age groups: 22 to 38, 39 to 49 and 50 to 74 years. We measured electrocardiogram, arterial blood pressure and laser Doppler (LD) flux of cutaneous microvessels in response to local warming of the skin to 42°C. Data were analysed using ANOVA followed by Dunnett’s test. The criterion selected for a statistically significant difference was p-value less than 0,050. The study was approved by the National Medical Ethics Committee; written informed consent was obtained from each subject. RESULTS. There were no differences in RR-intervals, systolic and diastolic blood pressure between patients and controls. At rest LD flux was statistically significantly higher in the group of 39-49 years old healthy control subjects than in APS patients of the same age. Vasodilatory response to local heating was significantly smaller in patients than in healthy subjects in the age group of 22 to 38 years (44.4 ± 16.1 PU in patients vs. 95.4 ± 20.2 PU in age matched controls) (t-test, p<0,050). In both older age groups (39-49 and 50-74 years) of APS patients and controls vasodilation was approximately the same (59.3 ± 9.3 PU in patients aged 39 to 49 vs. 57.7 ± 9.5 PU in age matched controls and 43.1 ± 11.3 PU in patients aged 50 to 74 vs. 55.6 ± 18.9 PU in age matched controls). CONCLUSIONS. From our research it can be concluded that the microcirculation in patients with APS is diminished. For more precise definition of these changes further research is required, which should take into account other characteristic of patients and health controls, as for instance the way of living, training, treatment of APS and other diseases such as hypertension etc.