Orange roughy (Hoplostethus atlanticus) occurs in commercially fishable concentrations along the northern Chatham Rise, east of New Zealand. In preliminary analyses for mercury, the mean level in the flesh coincided exactly with the maximum permissible level of 0.5 mg/kg set by the New Zealand Department of Health for fish sold on the local market. Because of its export potential, more detailed studies followed. Flesh samples of orange roughy were collected at sea and from a number of fish factories around New Zealand. Samples were taken at 2 depths below the skin to determine whether mercury was associated with the waxy subcutaneous layer. No significant difference was detected, but the variability in mercury levels between 2 of the sampled groups was found to be significant and was attributed to fish from different size ranges being analysed. The lower figure (0.35 mg/kg) was obtained from fish with lengths representative of the commercial catch. It is recommended that this value be officially accepted as the mean mercury level for orange roughy flesh.