It has been claimed that the incidence of postoperative hypothyroidism after subtotal thyroidectomy is higher in those patients whose thyroids show more extensive lymphoid infiltrate (Whitesell and Black, 1949;Greene, 1950 and1953;Levitt, 1951;Hargreaves and Garner, 1968). Since these reports were based on semiquantitative measurement methods, we have re-investigated this problem using the more accurate histometric technique. This paper reports our findings on the relation of the extent of thyroiditis to the preoperative drug treatment regime and to the incidence of postoperative hypothyroidism. Material and Methods CLINICAL INVESTIGATIONSThis study was undertaken on 95 female primary