The objective of this research was to identify chromosomal regions harboring QTLaffecting reproduction in pigs. A three-generation resource population wasdeveloped by crossing low-indexing pigs from a randomly selected control line(C) with high-indexing pigs of a line selected for increased index of ovulationrate and embryonic survival (I). Differences between Lines I and C at Generation10 were 6.7 ova and 3.3 fetuses at 50 d of gestation and 3.1 fully formed and1.6 live pigs at birth. Phenotypic data were collected on F2 females, born inthree replicates, for ovulation rate (n = 423), age at puberty (n = 295), littersize (n = 370), and number of nipples (n = 428). Litter-size data includednumber of fully formed, live, stillborn, and mummified pigs. Grandparent, F1,and F2 animals were genotyped for 151 microsatellite markers distributed acrossall 18 autosomes and the X chromosome. Genotypic data were available on 423 F2females. Average spacing between markers was 19.3 Kosambi centimorgans.Calculations of logarithms of odds (LOD) scores were by least squares, and fixedeffects for sire-dam combination and replicate were included in the models.Genome-wide significance level thresholds of 5% and 10% were calculated using apermutation approach. There was evidence (P < 0.05) for QTL affecting ovulationrate on SSC9, age at puberty on SSC7 and SSC8, number of nipples on SSC8 andSSC11, number of stillborn pigs on SSC5 and SSC13, and number of fully formedpigs on SSC11. There was evidence (P < 0.10) for additional QTL affecting age atpuberty on SSC7, SSC8, and SSC12, number born live on SSC11, and number ofnipples on SSC1, SSC6, and SSC7. Litter size is lowly heritable and sex-limited.Therefore, accuracy of selection for litter size may be enhanced bymarker-assisted selection. Ovulation rate and age at puberty are laborious tomeasure, and thus marker-assisted selection may provide a practical andefficient method of selection.