The influence of light and nutrition on fruit body development in Ascobolus biguttulatus was studied. High C and N concentrations inhibited sexual reproduction. A wide variety of carbon sources supported the production of fertile apothecia. Among the nitrogen sources, urea and asparagine were the best, while inorganic salts resulted in very poor fruit body production. Light was an absolute requirement for apothecial production. When photoinduction was accomplished by single 24-h periods, the colonies were most receptive at the 5th day of growth. Among types of light, near ultraviolet light was the most effective.