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We have constructed a quadrupole ion trap time-of-flight mass spectrometer to study photo-induced dissociation (PID) of biologically important molecules in the gas phase. The performance and capabilities of the mass spectrometer were investigated by measuring the mass spectra of protonated peptide ions produced by electrospray ionization. The typical mass resolution (m/Dm) was around 1000 and the collection efficiency measured for photo-fragment ions of protonated Tyr-Ala ions (YAH+) was about 41%. The PID spectra of YAH+ and protonated Gly-Trp ions (GWH+) were compared to their respective spectra obtained by collision-induced dissociation in the same instrument. The chromophore effect in photodissociation of protonated peptide ions was addressed with the PID spectrum of GWH+.