The incidence of Ascaris ova in sewage sludges at various Johannesburg Sewage Disposal Works has been investigated. The results indicate that the high infestation of the Native population with A. lumbricoides is responsible for the high incidence of Ascaris ova in sewage sludge. The relative viability of Ascaris ova in various types of sewage sludges has been determined experimentally, by culturing samples of sewage and sewage sludges containing Ascaris ova under laboratory conditions. It has been concluded that only the treatment and eventual cure of the carriers of ascariasis will finally result in an appreciable reduction in the number of Ascaris ova found in sewage and sewage sludges under present conditions. The proposed sterilization of sewage sludges will convert sludge into a safe fertilizing material, but it will eliminate the risk of infection from this one source only.