In this work, room-temperature phosphorimetry using cellulose substrates was evaluated as analytical technique for the determination of two indol derivatives (2 methyl indol and 7 methyl indol). The phosphorescence from both analytes were studied in a univaried way in function of several experimental parameters such as the phosphorescence decay rate; type and quantity of phosphorescence inducer (heavy atom salt); amount of surfactant used as cellulose surface modifier and the influence of the hidrogenionic concentration of the analyte carrier solution. Once defined the relevant factors, central composite designs were performed in order to obtain response surfaces that pointed out possible interactions among factors and lead to the best experimental conditions. For 2 methyl indol, the best conditions were achieved by using ethanol/water analyte carrier solution at its original pH, and substrates containing TlNO3/SDS or KI. Simillar conditions were found for 7 methyl indol. For each of the selected conditions, studies were performed aiming to find the analytical figures of merit which included: selectivity, linearity of the working range, limit of detection, limit of quantification, accuracy, precision, robustness and the uncertainty of the phosphorescence measurement from the solid substrate. In all cases, the linear response presented a linear behavior in function of the mass of the analytes placed on the substrate [R(2) > 0,99]. Limits of detection (blank signals average + 3sb) and limits of quantification (blank signals average + 10sb) were in the mol L(-1) range (absolut values of tenths of ng). The repeatability of the method presented values between 15 and 23%, being the main components of the phosphorescence measurement, which were calculated based on the procedure indicated in the ISO GUM. The uncertainty value was between 22 and 35% (combined uncertainty) epending on the experimental condition and on the analyte used in the calculation process. The selectivity towards other indols (indol and 7 methyl indol) and other classes of nitrogenated polycyclic aromatic compounds was evaluated by comparing phosphorescence characteristics from these substances. While no discrimination was possible for the indols, selectivity in the determination of 2 methyl indol and 7 methyl indol in the presence of acridine, 7,8 benzoquinoline and quinoline) was found.