B38 bacterial strain, isolated from Tunisian soil showed a strong antimicrobial activity. Based on biochemical characterization and 16S rDNA sequence analysis, B38 strain was identified as Bacillus subtilis. Cell culture supernatant showed antibacterial activity against clinical isolates of methicillin-resistant Staphylococcus species and several Gram-positive and Gram-negative bacteria. Antifungal activity against phytopathogenic fungi was also observed. Antibacterial activity production started at early exponential growth phase, and maximum activity was reached at the stationary phase. This antibacterial activity was neither affected by proteases, lipase, and organic solvents, nor by surfactants. It was stable over a wide pH range and still active after autoclaving at 121 degrees C during 20 min. Thin layer chromatography followed by bioautography assay allowed the detection of four active spots with R(f) values of 0.30, 0.47, 0.70, and 0.82. The single spot with R (f) 0.30 showed antifungal activity, whereas the spots with R(f) values of 0.47, 0.70, and 0.82 exhibited antibacterial activity.