In 36 young Nigerian men, ventilatory capacity and the changes in ventilation, tidal volume and tidal P CO2 during oxic CO2-rebreathing have been measured. CO2 response lines and breathing rhythms have been determined and analysed in relation to the anthropometric and lung function data. Previous findings that Nigerian men have a substantially lower ventilatory capacity than Europeans at a standard height and age are confirmed. Breathing rhythms in Nigerians appear to be the same as in other ethnic groups studied. CO2-sensitivity varies with FVC, as found previously in Europeans and New Guineans. However, at a standard FVC of 41, Nigerian men have the same CO2-sensitivity as Europeans, and not a lower value like New Guineans.