The reproductive cycles of Mytilus chilensis vary latitudinally. This species has reduced genetic and morphological differentiation due to its high potential for dispersal. Broodstocks from Yaldad Bay (Chiloe) and Zenteno Bay (Punta Arenas) were conditioned at 9 +/- 0.5 degrees C and 15 +/- 0.5 degrees C, and were fed a diet (1: 1) of Isochrysis galbana and Chaetoceros neogracile. We expected to determine whether conditioning at different temperatures produces changes in the reproductive potential of the populations. Gonadal development was lowest in the broodstocks conditioned at 9 degrees C, and highest in those conditioned at 15 degrees C, from Chiloe. Fertility was greater in broodstocks from Yaldad than in those from Zenteno. Oocyte diameter was greater in broodstocks from Zenteno, and both populations showed larger diameters at 9 degrees C. Neither the percentage of fertilized eggs nor the percentage of larvae hatching differed significantly between populations at either conditioning temperature. Therefore, it was not possible to establish differences in the reproductive potential of the populations under the conditions studied herein.