The inheritance of congenital goiter due to a thyroglobulin synthesis defect in a strain of Dutch goats has been studied by Mendelian and biochemical methods. Mendelian analysis of 301 matings, resulting in 591 kids, showed an autosomal recessive mode of inheritance. A restriction fragment length polymorphism (RFLP) in the thyroglobulin gene also was used to confirm the recessive mode of inheritance of the defect. In a pedigree consisting of 27 goats, spanning four generations, the genotype determined by RFLP study was in accordance with the observed phenotype and the autosomal inheritance of the defect. Although phenotyplcally no differences were detected between normal and heterozygous animals, the use of RFLPs allowed the diagnosis of the three genotypes.