Algae cultivation is the essential basis for microalgal biofuel production. Soluble algal products (SAP) are significant obstacle to large-scale, high-cell-density cultivation processes. SAP accumulation during batch cultivation of Scenedesmus sp. LX1 (a unique strain accumulating lipid substantially while growing fast under low-nutrient conditions) with different initial nitrogen concentrations (7.4-34.0 mg N L-1) was investigated. The SAP content varied in the range of 3.4-17.4 mg DOC L-1 at stationary phase, with average yield per cell of 0.5-2.5 pg DOC cell(-1). High SAP accumulation up to 15.2-17.4 mg DOC L-1 were observed with initial nitrogen above 20.2 mg N L. The maximum SAP production rate per unit culture volume (r(SAP)) was 2.6 mg DOC (L d)(-1) and that per cell (nu(SAP)) was 1.5 pg DOC (cell d)(-1). The r(SAP) increased with cell growth rate and decreased with cell density linearly. The SAP accumulation was majorly due to the release of growth-associated products. (C) 2011 Elsevier Ltd. All rights reserved.