This work shows that diffuse reflectance measurements, using fiber optical devices, can give rapid quantitative results for application with spot tests determination where little sample manipulation is a desirable feature. The experiments were performed with a Hewlett Packard diode array spectrophotometer HP8452A and a Labsphere RSA-HP-84 reflectance accessory. The quantitative reflectance measurements of different complexes such as Fe (III) with thiocyanate, Cr (VI) with diphenylcarbazide and Ni (II) with dimethylglyoxime could be obtained by forming the complexes on filter paper. Calibration curves were obtained for each metal by plotting the optical density of the reflectance signal (AR) vs. the log of the mol/dm3concentration, from 1.5 × 103to 3.6 × 102mol/dm3for Fe (III), from 8.00 × 10−5to 2.00 × 103mol/dm3for Cr (VI) and from 1.00 × 103to 8.00 × 102mol dm3for Ni (II), with correlation coefficients of 0.9986 for Fe (III), 0.9878 for Cr (VI) and 0.9892 for Ni (II). The results obtained show that it is possible to perform quantitative spot-test analysis using reflectance measurements in the visible region of the spectrum.