Cotes, J. E., Dabbs, J. M., Hall, A. M., Axford, A. T., and Laurence, K. M. (1973). Thorax, 28, 709-715. Lung volumes, ventilatory capacity, and transfer factor in healthy British boy and girl twins. Normal values are reported for the lung volumes, ventilatory capacity, and transfer factor of 212 healthy British twin children aged 8 to 16 years. The boys and the girls share a common relationship to height for the residual volume, peak expiratory flow rate, and Kco (transfer factor per litre of lung volume). For the inspiratory capacity and the transfer factor, also its membrane component (Dm), the values for the boys exceed those for the girls by, on average, 10%. This difference may be due, at least in part, to the boys taking more exercise.