Reproductive aspects of the horse mackerel in Chilean waters were determined from 309 specimens collected between January 1963 and April 1964 in three fishing locations. Changes in the gonadosomic indices, condition factors, and distribution curves of egg sizes indicated that horse mackerel spawned in December in Antofagasta and in February in Coquimbo and Valparaiso. Spawning lasts probably less than a month. Female horse mackerel may spawn for the first time in their third year of life (about 36 cm fork length and 600 grams body weight). Four-year-old females were, in general, adults. Large variation in the fecundities of fish of similar size and weight, respectively, was found. Five-year-old females contained an average of 639,105 yolked eggs. The average number of yolked eggs per gram of fish was greater in Coquimbo (590) than in Antofagasta (383) and Valparaiso (332).