Microcirculatory homeostasis was studied in 107 children suffering from rheumatic fever. Conjunctival microcirculation and platelet aggregation were examined. The content of circulating immune complexes and medium-size molecules was measured in the blood. Microcirculation was investigated in 137 healthy children aged 3 to 15 years, making up a control group. Comprehensive investigation of microcirculation in children suffering from rheumatic fever enables one to define the activity of the rheumatic process at the early times of the illness and to ensure timely administration of adequate antirheumatic therapy.