Microsatellite DNA markers were used to investigate levels of genetic diversity within cultured populations of Haliotis midae and Haliotis rubra in South Africa and Australia, respectively. The cultured populations examined were F1 progeny of wild caught broodstock. All populations show a decline in genetic diversity, measured as the number of alleles per locus (35-62% allele loss) when compared to wild stocks in the area of respective broodstock collection. There was, however, no associated loss of heterozygosity. Changes in the frequency of alleles between farmed and wild samples were observed in both species. Mean levels of genetic relatedness for the cultured H. midae were not significantly different to zero, while those for the cultured H. rubra were significantly higher. The estimated effective population size of H. midae broodstock was between 75.3 (SD±57.6) and 43.5 (±29.8) for a west coast farm and between 18.5 (±8.4) and 16.8 (±8.0) for an east coast farm. The observed loss of alleles in both farm samples was significantly greater than that expected due to genetic drift based on such effective population size estimates. The effective population size of a farm sample of H. rubra was estimated at between 27.2 (±3.8) and 22.4 (±4.7). The observed loss of alleles in this instance was not significantly greater than expected due to genetic drift.