Both biofilms and planktonic (suspended) cells of Candida albicans synthesized extracellular prostaglandin(s) during growth at 37 degrees C, but biofilm cells secreted significantly more prostaglandin(s) when production was determined on the basis of cell dry weight. Prostaglandin synthesis by both cell types was sensitive to the cyclooxygenase inhibitors aspirin, diclofenac and etodolac. A morphological mutant blocked in two signalling pathways (cph1/cph1 efg1/efg1) produced prostaglandin levels similar to those of the parent strain, but formed yeast-only biofilms. These results suggest that prostaglandin production could be a significant virulence factor in biofilm-associated infections, although its role in C. albicans morphogenesis remains unclear.