Production of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) concentrates from tuna oil was optimized. In the process, the liquid recovery yield (Y-1) and the total content of DHA and EPA (Y-2) were response variables, respectively. A three-factor central composite rotatable design (CCRD) was used to study the effect of urea-to-fatty acid ratio (XI), crystallization temperature (X-2) and crystallization time (X-3). Second order polynomial regression models for Y-1 and Y2 were employed to generate response surfaces. The total DHA and EPA (85.02%) and the liquid recovery yield (25.10%) from tuna oil were obtained at a urea-to-fatty acid ratio of 15 (mole/mole), a crystallization temperature of -5 degrees C, and a crystallization time of 20 h. (c) 2005 Elsevier Ltd. All rights reserved.