The lipase produced by Pseudomonas glumae is monomeric in the crystalline state and has a serine protease-like catalytic triad; Ser87-His285-Asp263. The largest domain of the protein resembles closely a subset of the frequently observed alpha/beta-hydrolase fold and contains a well-defined calcium site. This paper describes structural analysis of this protein, focusing on (i) structural comparison with the lipase from Geotrichum candidum, (ii) the probable nature of the conformational change involved in substrate binding and (iii) structural variations amongst the family of Pseudomonas lipases. This analysis reveals similarities between P. glumae lipase and G. candidum lipase involving secondary structural elements of the hydrolase core and the loops carrying the catalytic serine and histidine residues. A possible functional equivalence has also been identified between parts of the two molecules thought to be involved in a conformational change. In addition, determination of the structure of P. glumae lipase has allowed rationalization of previously reported protein engineering experiments, which succeeded in improving the stability of the enzyme with respect to proteolysis.