Direct contact membrane distillation was used for the separation of saline wastewater. Wastewater containing NaCl and protein as well as the effluents produced during the regeneration of ion exchangers was used as feed. During the concentration of these solutions by the membrane distillation process, severe fouling of the membranes was observed in several cases. The major reasons for fouling were associated with heating of the feed and increasing concentration of solutes. The membrane morphology and composition of the fouling layer were studied using scanning electron microscopy coupled with energy dispersion spectrometry. The application of appropriate pretreatment enabled the removal of foulants from the feed; hence the treatment of such wastewaters by membrane distillation was possible.