A closed population of juveniles was studied to follow-up manifestations of primary rheumatic fever. In line with other unfavourable factors, the onset of the disease within the first 6 months of the observation was due to cross streptococcal infection (foci of chronic nasopharyngeal infection were detected in 68.6% examinees, rheumatism debut after acute nasopharyngeal infection was in 91.0% patients). Persistence of streptococci was established in many blood counts in immunofluorescence reaction in 88.2% patients in acute disease, in more patients with lingering rheumatic process. Clinical manifestations include, aside from arthritis and rheumocarditis, frequent thyroid and gastrointestinal lesions. It is thought valid to raise the dose and duration of administration of penicillin in patients with primary rheumatic fever as it eradicates chronic infection foci, prevents recurrences, reduces the number of patients with a lingering course of the disease, with recurrences and valvular defects of the heart.