Ascaris suum eggs, due to their inherent environmental indestructability, are routinely used as bio-indicators to test the ovicidal activity of various manure and biosolids disinfection methods. Exposure to organic acid is a possible disinfection method of inactivati ng Ascaris eggs. Previous research has shown the eggs could readily be killed when the pH of the acid solution was below the pKa of the acid, where most of the acid is in the undissociated form. Expanding on this earlier work, various concentrations and c ontact times of butanoic, pentanoic, hexanoic and heptanoic acid, with and without 18 mM Tween 20 at pH 4, were examined to determine m inimum required times for total inactivation at 22°C and 37°C. Increasing the temperature by 15 degrees caused a significant decrease in the contact time required for total inactivation. The results suggest that higher concentration of pentanoic and hexanoic acids with or without the addition of the surfactant Tween 20 have potential for the rapid inactivati on of helminth eggs in soil and water. Treating with acids with added surfactant, Tween 20, did not have any significant effect on egg inactivation in case of both lower and higher concentration and in both temperature.