The species composition of by-catch was studied in the Spanish Greenland halibut (Reinhardtius hippoglossoides) fishery, developed in the NAFO Regulatory Area in Div. 3L, 3M and 3NO, for the period 1991–94. Of the 17 species occurring in the catches, two groups were identified as the more and less frequent species. The more frequent species with an annual yield of about 5 kg/hr were roughhead grenadier, roundnose grenadier, skate, American plaice, redfish, witch flounder and blue antimora. Analyzing the data on a monthly basis revealed some species such as grenadiers, skate and American plaice, particularly in Div. 3N, did not change much while other species had increased yields in recent years. The characteristic species of the demersal fisheries (skate, American plaice) showed a wide bathymetric distribution. The transfer of effort southwards to Div. 3NO in recent years, mainly in the case of small vessels, has meant variation in the composition and relative abundance of by-catch in this fleet. The proportion of each by-catch species was highly variable. Skate, American plaice, witch flounder and grenadiers were caught most frequently in both fleets. In the large vessels, however, blue antimora, redfish and roundnose grenadier were more frequent than in the small vessels. The length distribution in the discarded proportion was analyzed for the two grenadiers, skate and blue antimora. In general, the length distribution of the proportion discarded showed a wide range.