1. We previously reported loss of heterozygosity (LOH) at region q13 of chromosome 11 in five aldosterone-producing tumours (APT) using restriction fragment length polymorphism (RFLP) analysis, including two from patients with familial hyperaldosteronism. 2. In the present study, microsatellite markers were used to examine 33 informative paired blood and tumour DNA samples from patients with APT for LOH at three loci that map to chromosome 11q13. 3. LOH at one or more loci was detected in seven (21.2%) tumour DNA samples. 4. This study provides further support that mutations at 11q13 may be involved in the underlying pathophysiology of aldosterone-producing tumours of the adrenal cortex.