We compared three different scintigraphic techniques for the localization of neck recurrences and metastases in seven patients with medullary thyroid carcinoma one month to eight years after the first surgical intervention. Three successive scintigraphic studies were performed in five patients (6 x 3 studies) within two weeks using 201Tl chloride, 111In-labeled F(ab')2 fragments of the anti-carcinoembryonic antigen (anti-CEA) monoclonal antibody (MoAb) BW 431/31, and 131I meta-iodo-benzylguanidine (MIBG). Additionally, 11 studies were performed with the 111In-labeled MoAb fragment BW 431/31 (seven studies) or the 99mTc-labeled intact anti-CEA MoAb BW 431/26 (four studies). The gold standards for classifying scintigraphic results were biopsy, histology, surgery, and cytology. Six regions were classified as positive or negative in each study: thyroid region, four quadrants (lymph node regions) around the thyroid, and the region of the upper mediastinum. Of 36 sites, 201Tl was true positive (TP) in seven sites, false-positive (FP) in one site, true negative (TN) in 22 sites, and false-negative (FN) in six sites, resulting in a sensitivity of 54% and a specificity of 96%. 131I MIBG was TP in four sites, FP in none of the sites, TN in 23 sites, and FN in nine sites, with a sensitivity of 31% and a specificity of 100%. Immunoscintigraphy (102 sites overall) was TP in 16 sites, FP in five sites, TN in 77 sites, and FN in four sites, resulting in a sensitivity of 80% and a specificity of 94%. Immunoscintigraphy with 111In/99mTc anti-CEA F(ab')2 fragment/intact antibody is superior to scintigraphy with 201Tl and 131I MIBG.