Effects of nitrogen (N) sources and their concentration on the accumulation of alpha-tocopherol of Nannochloropsis oculata (Eustigmatophyceae) were examined. Sodium nitrate and ammonium chloride were used as inorganic nitrogen sources at the concentrations of 882 mu mol 1(-1) and in half the strength of F/2 medium in N. Maximum content of alpha-tocopherol was 2325.8 +/- 39 mu g g(-1) dry weight (DW) in NO3--N in the medium. N. oculata grew rapidly at 882 mu mol 1(-1) concentration of NO3--N and NH4+-N in the medium and maximum cell numbers were obtained as 5.2 +/- 0.3 x 10(7) cells ml(-1) and 4.9 +/- 0.1 X 10(7) cells ml-1, respectively. The research showed that decreasing N concentrations led to an increase in alpha-tocopherol accumulation, but reduced growth rate. Significant differences in the alpha-tocopherol content of N. oculata were found to be dependant on factors such as; N source, concentration and growth phase. (c) 2007 Elsevier B.V. All rights reserved.