The patterns of gangliosides and phospholipids and their relation to TSH response were examined in twenty-six malignant thyroid tumors (4 follicular, 6 papillary, 5 medullary, 11 anaplastic carcinomas) and thirty-six hyperplastic goiters. Thirteen thyroid tissues adjacent to benign tumors with no evidence of macroscopic or microscopic abnormalities were used as normal tissue. In normal thyroids the major ganglioside was GD3(44%) and GM3 was the second ganglioside (20%). In minor amounts GD1a (8.6%), GD1b (6.2%), GT1b (5.7%) and GM1(5.6%) were present. In hyperplastic goiters and in follicular carcinomas the patterns of gangliosides were similar to that of normal tissue except for GM3 which, in the last tissue, was higher (34%). In papillary carcinomas low levels of GM3 (11%) and GT1b (0.8%) with a high level of GD1b (12.6%) were found. In anaplastic carcinomas GM3 was very high (47%) whereas GD3 was low (18%). In these tumors also a high percentage (14.0%) of GD1a was found. In medullary carcinomas the lowest levels of GM3 (4%) with the highest level of GD3 (64%) were found. Although large differences of the gangliosides distribution were clearly encountered in the various pathological human thyroid, no correlation between lack of TSH response and some individual ganglioside could be made. No differences in the individual phospholipid in the various tissues studied were found.