Chemical analysis of rhinovirus 14 revealed a ribonucleic acid (RNA) content of 29.8% and a high adenylic acid content (35%). A partial specific volume of 0.682 cm(3)/g was obtained for the rhinovirion. Rhinovirus and poliovirus had identical sedimentation coefficients of 158S. A diffusion coefficient of 1.71 x 10(-7) cm(2)/sec was consistent with a hydrated diameter of 25 nm for the rhinovirion. The calculated molecular weights of the rhinovirion and its genome were 7.1 x 10(6) and 2.1 x 10(6) daltons, respectively. Sedimentation analysis of infectious RNA confirmed the similarity of the molecular size of the poliovirus and rhinovirus genomes.