Previously, we have shown that reference and freshly isolated Treponema denticola cultures are capable of metabolising cholesterol, progesterone, 4-androstenedione and testosterone by means of 5alpha-reductase, 3beta-and 17beta-hydroxysteroid dehydrogenase activity [Clark DT, Soory M. The metabolism of cholesterol and certain hormonal steroids by Treponema denticola. Steroids. 2006;71:352-63. ]. The aim of the work presented in this paper was to investigate the modulation of T. denticola growth in batch cultures by these steroids, using T. denticola ATCC 33520 as a model system. Growth curves were summarised using statistics based on optical density and protein yield. Cholesterol was found to stimulate growth at concentrations of 10 and 25microg/mL. Certain hormonal steroids inhibited the maximum achievable optical density at concentrations of 1 and 10microg/mL while the minimum concentration shown to inhibit protein yield was 0.001microg/mL of progesterone. The potential of the hormonal steroids to inhibit growth was in the order of progesterone, 4-androstenedione and testosterone.