It had been reported that adjusting the pH of the suspension to pH 3 - 4 increases the effectiveness of the SPR.(4) The pH of SPR II solution was 3.1. The lowest quality of developed latent prints was obtained from SPR I and SPR VII which had a pH of 2.45 and 7.42, respectively. Thus, a suitable pH of the SPR reagent may be between 3 and 4, but this awaits confirmation. It has also been shown that in acid conditions, the enhancement of fingermarks with ninhydrin or cyanoacrylate was inhibited but SPR could be used instead.(5) Nevertheless, the present study demonstrated that under more acidic conditions the enhancement of latent prints with SPR was inhibited, as shown with SPR I (pH 2.45). Thus, pH is an additive factor that affects the SPR solutions.