Solid-state microcosms were used to assess the influence of constant and variable C/N ratios on the biodegradation efficiency by Aspergillus niger at high hexadecane (HXD) concentrations (180-717 mg g(-1)). With a constant C/N ratio, 100% biodegradation (33-44% mineralization) was achieved after 15 days, at rates increasing as the HXD concentration increased. Biomass yields (Y-X/S) remained almost independent (similar to 0.77) of the carbon-source amount, while the specific growth rates (mu) decreased with increasing concentrations of HXD. With C/N ratios ranging from 29 to 115, complete degradation was only attained at 180 mg g(-1), corresponding to 46% mineralization. Y-X/S diminished (similar to 0.50 units) as the C/N ratio increased. The highest values of mu (1.08 day(-1)) were obtained at low C/N values. Our results demonstrate that, under balanced nutritional conditions, high HXD concentrations can be completely degraded in solid-state microcosms, with a negligible (< 10%) formation of by-products. (c) 2005 Elsevier Ltd. All rights reserved.