Mutants of human rhinovirus type 2 (HRV-2) resistant to and dependent on the antirhinoviral compound chalcone Ro 09-0410 were selected in cell culture under clean laboratory conditions. A total of 42 volunteers were challenged with either the drug-resistant mutant [SR2-410(r)] (15 volunteers), the drug-dependent mutant [SR2-410(d)] (15 volunteers), or a wild-type HRV-2 which had a similar passage level in vitro as the mutants but without the drug (12 volunteers). Of volunteers challenged with the wild-type HRV-2, 33, 67, and 82% developed cold symptoms, shed virus, and showed serological evidence of infection, respectively. In contrast, only 13, 27, and 23% of volunteers challenged with the drug-resistant mutant developed colds, shed virus, and showed serological evidence of infection, respectively. None of the volunteers challenged with the drug-dependent virus became infected or had symptoms of colds. These results demonstrate that a drug-resistant rhinovirus was capable of infecting humans and producing disease, although its infectivity was reduced when compared with that of the wild type. In contrast, a drug-dependent virus had lost its ability to infect humans.