The patterns of disease caused by five common viruses which infect the respiratory tract are described. The viruses were strains of rhinovirus types 2, 9, and 14, a strain of coronavirus type 229E and of respiratory syncytial virus. Volunteers were given nasal drops containing a low infectious dose of one of the viruses, quarantined from 2 days before to 5 days after inoculation, and examined daily by a clinician using a standard checklist of respiratory signs and symptoms. Only subjects who developed clinical illness accompanied by viral shedding and/or specific antibody production were analysed [n = 116]. The results confirm indication from earlier studies that the main difference between colds induced by different viruses is in duration of the incubation period. Patterns of symptom development were not substantially different with different viruses. Analyses of signs and symptoms in different categories, e.g. nasal symptoms v. coughing, justify treatment with different drugs either successively or simultaneously.