Common cold is a most common disease in man accompanied by an experience of a diminished sense of smell. Controlled studies of the sense of smell are lacking and the cause as well as degree of impairment of smell in common cold has not been satisfactorily evaluated. We have investigated whether impaired olfactory ability accompanies common cold and if the loss is related to nasal blockage and to the amount of nasal discharge. For this purpose we measured the threshold of olfaction in volunteers before and after nasal inoculation with coronavirus 229E. The absolute olfactory threshold was assessed by a modified discrimination step test with dilutions of butanol. Symptoms of common cold were registered using a four-grade scale. Nasal obstruction was measured by nasal peak expiratory flow and by acoustic rhinometry and nasal discharge by weight of pre-weighted handkerchiefs. Individuals with a cold had impaired olfaction and the change in smelling ability correlated to the nasal congestion but not to the nasal discharge in analysis of multiple linear regression.