To demonstrate photodynamic antimicrobial chemotherapy (PACT) against planktonic and biofilm cultures of Pseudomonas aeruginosa, using photoporphyrin IX which could be endogenously synthesized by administrating delta-aminolaevulinic acid (delta-ALA), and a light emitted diode (LED) array to photoactivate the photosensitizer. P. aeruginosa suspended cells or biofilms, grown on a rotating disk reactor, were treated by different concentrations of delta-ALA in the dark for 1 h, followed by LED irradiation for various time. Regrowth experiments were conducted by placed PACT-treated disks back to a sterile reactor. Viable cells were determined by serial dilution and plate counts. Both P. aeruginosa planktonic and biofilm cells were inhibited by PACT with light doses or photosensitizer concentrations increasing. Treatments of planktonic cells with 10 mM delta-ALA and incident dose 240 J cm(-2) or 7.5 mM ALA and incident dose 360 J cm(-2) led to completely photoinactivation. No viable biofilm cells were found after treatment of 20 mM delta-ALA and incident dose 240 J cm(-2). However, regrowth was observed once PACT-treated biofilms were put back to a sterile reactor. Regrowth could be prevented only if biofilm samples were treated PACT twice. delta-ALA-mediated PACT on P. aeruginosa planktonic and biofilm cells was effective, though the detailed mechanism still required further investigation.