The use of ortho- and para-phenylenediamine (OPD & PPD respectively) for the enhancement of fingerprints in blood has been investigated. Optimal pH conditions and H₂O₂ concentrations have been determined using UV/Vis spectroscopy. Both OPD and PPD are effective and less hazardous alternatives to the presently used 3,3'-diaminobenzidine (DAB) for the development of blood fingerprints, especially on porous surfaces. The orange color of OPD and the purple color of PPD offer alternative colors to the brown color of DAB and the light green color of ABTS for standing out against particular backgrounds. Both OPD and PPD can be used after ninhydrin treatment, but the reverse is not the case.