The development of pneumatisation in the postcranial skeleton has been investigated in a flock of Golden Comet pullets from hatching to 182 days posthatching. The timing of development of pneumatisation in the vertebral column, vertebral ribs, sternum and humerus has been demonstrated. No pneumatisation was encountered in the sternal ribs, os coxae or coracoid. Development of pneumatisation in the coracoid and humerus was also studied in a flock of White Leghorn pullets and cockerels from hatching to 126 days posthatching. In this group, regular pneumatisation of the humerus occurred after the time of onset and the coracoid was frequently pneumatised unlike the Golden Comets. The rate of development of pneumatisation in the humerus was more rapid in White Leghorn pullets than in cockerels and also more rapid than in Golden Comet pullets.