The sexual calling incidence of wild and mass-reared Mediterranean fruit fly males, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), was studied at 25 °C and a photophase of 14 h starting at 0600 h. Wild males fed on yeast hydrolysate and sugar attained sexual maturity earlier and exhibited higher calling activity than males fed on sugar alone. In both sugar and yeast hydrolysate-fed wild males, calling levels were high during the first hours of the photophase, declined at 0900–1000 h, then increased again reaching high levels between 1200 and 1500 h, and finally declined and ceased after 1600 h. Food deprivation for 8 h or more caused a significantly lower frequency of calling. Irradiated (sterile) and unirradiated mass-reared males fed on either sugar and yeast or sugar alone did not differ in the age of attaining sexual maturity (maximum levels of calling occurred about 8 days earlier than in the wild males). However, irradiated males fed on sugar called less frequently than males in the other treatments of mass-reared males. The daily rhythm of calling in protein and sugar-fed irradiated males differed somewhat from that of wild males. Calling was recorded at high levels from the beginning of the photophase until 1300 h without any decrease at 0900–1000 h. It then decreased to very low levels from 1500–1800 h and increased slightly at 1900 h. These findings are discussed in relation to the mating behavior of the fly and to the effectiveness of released sterile males in Sterile Insect Technique programs.