The marine microalga Pavlova salina (Haptophyta, Pavlovophyceae) produces lipids containing approximately 50% n-3 long-chain polyunsaturated fatty acids including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). A full-length cDNA sequence, designated PsElo5, was isolated from P. salina. Sequence alignment showed that the gene was homologous to corresponding ELO-type elongases from other microalgae. Heterologous expression of PsElo5 in yeast and in higher plants confirmed that it encodes a specific Δ5-elongase activity as predicted and, furthermore, within the n-3 pathway, the elongation activity was confined exclusively to EPA.