The past decade has seen substantial breakthroughs in understanding the biochemistry, molecular biology and regulation of nitrate reductases (NR) in higher plants and green algae. In contrast, although there has been considerable interest in using various measurements of NR to provide ecophysiological information, comparable knowledge of NR is largely lacking in algal groups other than chlorophytes. Applying information about NR from chlorophytes and higher plants to other algae may be difficult. There is evidence that non-chlorophyte forms of NR are diverse and distinct in terms of biochemical characteristics and regulatory features. Key areas to be pursued in non-chlorophyte algae include the identification and adoption of model organisms for NR research in different algal groups; the creation of selected and engineered mutants; the purification, biochemical characterization and production of antibodies to different algal forms of NR; the identification of NR genes; and the undertaking of coordinated research on nitrate uptake proteins and other enzymes in pathways of nitrate assimilation.