Physical and nutritional factors required for growth of Bacteroides nodosus isolates from ovine foot-rot lesions were examined. Simplified anaerobic culture techniques were devised utilizing a fully soluble, autoclavable, liquid medium (TAS) which contained proteose-peptone, yeast and meat extracts and certain other essential compounds required to promote prompt and serially transferrable growth of cultures from small inocula. The latter included Trypticase, arginine, a reducing agent (most suitably thioglycollic acid) and CO2; serine and Mg2+ markedly increased growth yields. Trypticase could not be replaced by a commercial preparation of acid-hydrolysed casein; other forms of hydrolysed protein gave delayed and inconsistent growth. Maximum growth of cultures required concentrations of 0-02 to 0-35 M-arginine, which could not be replaced by glutamic acid, citrulline or ornithine. Exogenous carbohydrate compounds were not required. The temperature range for optimum growth of cultures was 37 to 39 degrees C, and anaerobic culture conditions were essential for growth and the production of B. nodosus organisms of normal morphology. Solidified TAS media for the isolation and maintenance of B. nodosus cultures were also devised.