Seven DNA markers from the pericentromeric region of chromosome 10 were tested for linkage to MEN 2A in a panel of 17 families. Four of the markers proved to be tightly linked and therefore suitable for predictive testing. The markers were used to estimate carrier risks for individuals who had a negative biochemical screening test for thyroid C-cell hyperplasia. The analysis substantially altered the carrier risks of most of these individuals, which suggests that typing with DNA markers should be introduced into the screening programme of MEN 2A families. Accurate prenatal diagnosis for this disorder is also now possible.