This method is for determining the approximate concentration of pyrroles and indoles having at least one hydrogen per carbon atom in the heterocyclic ring by visible spectrophotometry. It is applicable to gasolines, naphthas, kerosines and distillate burner oils, but is not applicable to crude and vacuum gas oils which are not completely soluble in n-heptane. Carbazoles and tetra substituted pyrrole, if present, are not determined. Olefins interfere with the determination and must be removed prior to analysis. Aromatic amines or aliphatic mercaptans can interfere with the test. The working range is 1 to 2000 mass-ppm pyrrole nitrogen.