The general incidence of whooping-cough is lower in fully immunised children, but present immunisation schedules do not adequately protect the infant below 1 year of age either from contracting infection or from its complications. In a recent outbreak in Glasgow, nearly one-third of notified cases were fully immunised. In Glasgow and probably in the U.K. as a whole, the persistance of whooping-cough in some areas is more strongly correlated with adverse socio-economic conditions that with lack of immunisation. The decline in recent years could be attributable to improvement in these conditions at least as much as to immunisation. There is no epidemiological justification for continuing mass immunisation, but there is a strong case for an intensified eradication policy which might include selective immunisation in high-risk groups and areas.