Xanthomonas campestris cells present in xanthan fermentation broth were lysed by enzymes secreted by Trichoderma koningii. Protease which appeared responsible for cell lysis was produced by the fungus in solid-state fermentation of wheat bran optimally at pH 7 and 30 degrees C in 72 h. The culture filtrate, having protease in addition to other extracellular enzymes, was used as such to clarify xanthan solution and found to lyse the cells optimally at pH 7 and 50 degrees C. The maximum transparency of xanthan solution achieved was 63%.