Orange and potato peels were studied in terms of their chemical compositions and their ability to support the growth and extracellular hydrolytic enzyme production of Bacillus subtilis strain 11089. The orange and potato peel substrates were prepared by blending and removal of large particles by filtration. The chemical composition of the filtrates were similar to the crude peel ＇starting＇ material and were shown to contain predominantly alcohol-insoluble solids (pectin, cellulose, starch), soluble sugars and minerals (mainly Ca, K, P, and Si). The composition of the orange peel (substrate) was different to that of the potato peel (substrate) mainly in terms of low levels of starch and protein, and higher levels of sugars, pectins and cellulose. Bacillus species 11089 was capable of growth in continuous culture on both orange and potato substrates when these were used as the carbon-energy source in a mineral salts basal medium. Potato filtrate supported the highest growth (mu(max) and biomass yield) but lowest specific activities of ol-amylase, neutral and alkaline proteases, and polygalacturonate-lyase compared to orange filtrate as substrate; however, when enzyme activity was expressed as units per volume of culture, potato filtrate supported the highest levels. In all cases, enzyme production using the various filtrates alone or mixed (1:1) was similar to or better than that produced by glucose used at the equivalent weight-volume concentrations.