Although long known as a parasite of medical and veterinary importance, interest in Toxoplasma gondii has increased with its emergence as a major cause of death in immunosuppressed individuals, and with recognition of its suitability as a model system for molecular and cellular investigations of apicomplexan parasites. The NATO workshop brought together 32 scientists working in different areas of toxoplasmosis research to gain an overview of progress in the field. Molecular studies have been carried out on genomic and extrachromosomal DNA. They reveal that Toxoplasma is very highly conserved, genetic mapping is underway and preliminary linkage analysis suggests recombination is rare; moreover all virulent strains share