A very simple and low cost reflectometer, for colorimetric diffuse reflectance measurements is described. The proposed instrument uses a light dependent resistor (LDR), as a sensor, and a light emitter diode (LED), as light source. The performance of the device was compared with that of a commercial instrument, measuring the reflectance of the Pantone(R) Process Black Uncoated Palette. The quantitative analysis of nickel, in a catalyst, using dimethylglyoxime as colorimetric reagent, was also used to test the device. The observed precision was about 6% (R.S.D.). These results were compared with those obtained by the gravimetric method using the same reaction, through the statistical Student's t-test procedure. A complete agreement was observed. The good quality of all the obtained results allows the recommendation of the instrument for diffuse reflectance measurements including quantitative analytical procedures. (C) 2002 Elsevier Science B.V. All rights reserved.8816066