Temperature-sensitive mutants of human rhinovirus type 2 were isolated by random clonings of mutagenized virus. All mutants were stable. Temperature sensitivity was not affected by different host cell systems. Complementation was observed in 3 of 10 dual viral mixtures, with complementation indices being as high as 4.0. Recombination frequencies fluctuated widely between experiments with different mutants, but positive recombination occurred with mean frequencies ranging from 0.03 to 1.25%. The complementation and recombination results obtained are similar to those reported for other picornaviruses.