We obtained 100 isolates of bacteria from deep-sea mud samples collected at various depths (1050-10897m). Various types of bacteria such as alkaliphiles, thermophiles, psychrophiles, and halophiles were recovered on agar plates at a frequency of 0.8 x 10(2) to 2.3 x 10(4)/ g of dry sea mud. No acidophiles were recovered. These extremophilic bacteria were widely distributed, being detected at each deep-sea site, and the frequency of isolation of such extremophiles from the deep-sea mud was not directly influenced by the depth of the sampling sites. Phylogenetic analysis of deep-sea isolates based on 16S rDNA sequences revealed that a wide range of taxa were represented in the deep-sea environments. Growth patterns under high hydrostatic pressure were determined for the deep-sea isolates obtained in this study. No extremophilic strains isolated in this study showed growth at 60MPa, although a few of the other isolates grew slightly at this hydrostatic pressure.