Age involution in the normal human adult thymus

Thymic biopsies taken under general anaesthetic prior to partial thyroidectomy for non-toxic nodular goitre were studied with histometric techniques: evidence is presented that the tissue studied is representative of the normal adult human thymus. The pattern of age involution of the normal adult thymus is described: there is a striking sex difference in the curves of involution, due to differences in behaviour of the cortex.