We present the computer program HYBRIDLAB 1.0 for simulating intraspecific hybrids from population samples of nuclear genetic markers such as microsatellites, allozymes or SNPs (single nucleotide polymorphisms). The program generates a user-specified number of multilocus F1 hybrid genotypes between any pair of potentially hybridizing populations included in a standard input-file of multilocus genotypes for population genetic analysis. This simple, user-friendly program has a wide range of applications for studying natural and artificial hybridization; in particular, for evaluating the statistical power for individual assignment of parental and hybrid individuals. An example of application for Atlantic cod populations is given.