95 dermatophyte strains (12 of Trichophyton mentagrophytes, 12 of T. tonsurans, 11 of T. rubrum, 12 of T. megninii, 12 of T. violaceum, 2 of T. schoenleinii, 1 of T. soudanense, 12 of M. canis, 8 of Microsporum gypseum, 1 of M. ferrugineum and 12 of Epidermphoyton floccosum). 1 of Aspergillus niger, 1 of A. ochraceus, 1 of Paecilomyces sp., 1 of Penicillium sp. and 1 of Candida albicans were grown in Sabouraud liquid medium for the study of pH variation over 6 weeks at room temperature and after 4 weeks at 37 degrees C. All the dermatophyte strains alkalinized the medium. The highest pH values after 2-3 weeks' development in room temperature were produced by T. mentagrophytes, M. gypseum and M. canis, and the lowest by T. rubrum and T. violaceum. After the 4th week the alkalinizing activity became more marked for T. mentagrophytes and remained stationary for T. violaceum, In the 5th week the values produced by T. tonsurans were higher than those for M. gypseum, and those for E. floccosum and T. megninii were higher than those of M. canis. A similar behaviour was observed for T. rubrum and T. megninii and for M. canis, M. gypseum and M. ferrugineum. There seems to be a relation between the alkalinizing capacity and the rapidity and amount of the growth. At 37 degrees C both alkalinization and range of variation of the pH values of the medium became more noticeable for the strains of each species.