A convenient and rapid method for screening and identifying rod mutants of Bacillus subtilis is described. At the restrictive temperature (45 degreesC), all rod mutants of B. subtilis screened lost their ability to sporulate. The morphology and colour of mutant colonies grown on sporulation agar plates differed from those of rod(+) cells, which were able to sporulate even at elevated temperature. These characteristics provide an alternative approach for the identification of rod mutants in B. subtilis culture by streaking the cells onto a minimal glucose agar plate and incubating at the restrictive temperature. After 30 h of incubation at this temperature, rod mutants are easily identified. This method will facilitate the screening and isolation of rod mutants of B. subtilis.