Exogenous application of dilute hydrogen peroxide (H2O2) increases neutral lipid production in Phaeodactylum tricornutum. Exposing early stationary phase cultures of P. tricornutum to 0.25-2 mM H2O2 increases the amount of neutral lipids per biomass (mg/mg) by > 100% at 24 h post H2O2 treatment as determined upon lipid extraction and analysis using a neutral lipid assay. H2O2 treatment increased the total levels of neutral lipids harvested up to 50%, from 64 mg/L to 96 mg/L, demonstrating its possible effectiveness as a pre-harvest strategy to enhance the biofuel feedstock potential of P. tricornutum. The effects of H2O2 on biomass are concentration dependent; increasing concentrations of H2O2 reduce the levels of isolated biomass. Analysis of combined stressors demonstrates that H2O2 treatment exhibits synergistic effects to enhance neutral lipid production under nitrogen-depleted, but not phosphorus-depleted conditions, suggesting that the effects of hydrogen peroxide on lipid production are influenced by environmental nitrogen levels. (C) 2016 Elsevier Ltd. All rights reserved.