SummaryReport of a case of atypical viral pneumonia, with high cold agglutinin titer, complicated by hemolitic jaundice.Auto-and hetero-antibodies were detected in the serum. Direct Coombs test was positive. Those antibodies were only active at 40C.Rapid disappearence of circulating antibodies can be explained by their fixation on homologous tissue antigenic components and by specific inhibition by antibiotic of viral antigenic formation.