In a chronic experiment, male Wistar-rats were treated alone and in combination with methylthiouracil and lead acetate. Additionally, the animals of 2 groups were thyroidectomised. The suprarenal organs were investigated gravimetrically. Histologic-cytological and caryometrical investigations were made on the suprarenal cortex. After lead acetate application in the cortex, strong histologic-cytological alterations were obtained. There are marked damages especially in the zona fasciculata; a great number of pycnotic nuclei, a small subcapsular blastem, and a spreading out of the zona reticularis are observed. The size of nuclei is significantly diminished. These results indicated a regressive transformation and a toxic effect is discussed. After application of methylthiouracil or thyroidectomy, a regression transformation is found too. Cellular degenerations in all zones of the cortex are rarely or not obtained. As well methylthiourail as thyroidectomy diminish the weights of suprarenal organs high significantly. These results are not found after combined application of methylthiouracil and lead acetate. Methylthiouracil reduced the effect of lead acetate. The results allow to draw the following conclusion: In our opinion, a hypothetic methylthiouracil-lead-compound is built. This interpretation is supported by the persistent effect of lead acetate whenever lead acetate is combined with thyroidectomy.