New thermostable enzyme activities of seven Thermus strains were compared using the API ZYM system. All the strains exhibited high levels of alpha- and beta-glycosidases, esterase (C-4) and esterase-lipase (C-8) activities intracellularly. Only T. thermophilus HB8 (ATCC 27634) showed alpha-glucosidase and esterase activities in the supernatant. According to the intensity of beta-galactosidase activity, Thermus strains were divided in three groups. Group 0, which showed a weak beta-galactosidase activity, included Thermus spp. ATCC 31674 (T351) and 27978 (X-1) as well as T. thermophilus ATCC 27634 (HB8). Group I which consisted of T. aquaticus ATCC 25104 (YT-1), ATCC 25105 (Y-VII-51B) and Thermus sp, ATCC 27737 (T2), had a specific activity of approximately 40.0 U mg(-1) and galactose as inducer. T. aquaticus ATCC 31558 (group 2) was particularly effective for beta-galactosidase production (2840 U) with a specific activity of 98 U mg(-1). For each strain, galactose (0.5%) was a better inducer of beta-galactosidase production than lactose (1%). The detection of beta-galactosidase activity was dependent on the derivative chromogenic substrates used (naphthyl or nitrophenol coupled to sugar). Oligosaccharides were syn thesized from cellobiose, lactulose, maltose or lactose as substrates at high temperature in some strains of Thermus.