The tuberculin response in a crew of nearly 1,000 men on board a US Navy ship was investigated for a one-year period. The incidence of tuberculin conversion was found to be high even though no active tuberculosis was detected. Most of the men manifesting conversion had tuberculin reactions which were weak and highly variable. The reactions were similar to those attributed to atypical mycobacteria in several recently reported studies. Crossreactions from nontuberculous organisms must be considered when evaluating tuberculin test results obtained in the investigation of tuberculosis.