Motivation: Quick and easy gene mapping by the use of a panel of cytogenetically characterized somatic cell hybrids is possible, even if some discordant experimental results arise. Results: An interactive program is proposed and is made available on a WWW site to users of a somatic cell hybrid panel. Assignments to chromosomes and subchromosomal regions are based on likelihood calculations and Bayes' theorem, and a confidence level is provided. The method is illustrated in the case of the pig genome. Availability: The program can be accessed free of charge at URL http:/ /www. toulouse. inra.fr/lgc/lgc.html. Contact: E-mail: chevalet@toulouse.inra.fr