Because of the increasing knowledge of the physiological importance of biologically active amines in man and the importance of the presence of these amines in cheese, this study was done to obtain quantitative information for tyramine, tryptamine, and histamine in cheese available in the United States. The tyramine, histamine, and tryptamine contents of 156 samples of cheese purchased at retail stores were quantitated by thin-layer chromatography and fluorescence measurements of NBD-chloride derivatives of the amines. Tyramine was found in 81 of 85 Cheddar cheese samples examined. Extra-sharp, sharp, and medium Cheddar cheese samples contained average tyramine values of 0.27, 0.21, and 0.24 mg/g, respectively. Average tyramine contents were lower in mild and processed Cheddar (0.09 and 0.11 mg/g, respectively). The highest Cheddar cheese tyramine content was 0.7 mg/g. Tyramine was consistently found in all cheeses except in unripened soft cheese (Cottage). Histamine concentrations varied from nondetectable amounts to 2.6 mg/g in a Sap-Sago cheese sample. Twenty-four Cheddar cheese samples contained histamine with the highest amount being 1.3 mg/g. A domestic Blue cheese contained 2.3 mg/g. Tryptamine was uniformly low or completely absent in the Cheddar cheese samples. The highest tryptamine concentration (1.1 mg/g) was detected in a Blue cheese.