Atypical mycobacteria are important human pathogens. Although they often cause systemic disease, mycobacterial infection may present solely as cutaneous lesions. It is not easy to detect nontuberculous mycobacteria by the traditional histochemical Ziehl-Neelsen stain, or by culture on specific media. Polymerase chain reaction (PCR) may be used to identify nontuberculous mycobacteria in skin lesions. We report a 40-year-old man and a 36-year-old woman, both of whom were immunocompetent and kept fish, who had skin lesions on the backs of their right hands. Ziehl-Neelsen staining and culture on Lowenstein-Jensen media were negative. Mycobacterial DNA was detected by amplification of 16S ribosomal DNA. In both cases, PCR-enzyme-linked immunosorbent assay showed a positive signal when probes for Mycobacterium (universal probe) and M. chelonae were used, and in one patient M. fortuitum was also discovered. Antibiotic therapy with clarithromycin 500 mg twice daily was begun. After 6 months of treatment, the skin lesions were cured.