Summary Thermophilic bacteria of the genus Thermus were isolated from hot springs in Iceland. Growth factor requirement was tested for 24 strains. More than half of the strains would only grow in a minimal medium with single carbon sources if vitamins were also added. From a collection of about a hundred strains, 28 were used to test growth on 44 different single-carbon-source compounds. Nineteen compounds were not utilized by any of the strains. More than 70 % of the strains grew on galactose, maltose, acetate, pyruvate, α-keto-glutarate, asparagine, glutamate, glutamine and proline. The utilization of other compounds was variable and indicated a high degree of nutritional diversity among strains of Thermus .