The mol a r extinction coeffi ci ents for p-nitropheno 1 at pHs in the region of 8.0-9.2 in the presence and absence of various additives were determined. The data were statistically analysed. The validity and reprodu­ci bil ity of these values were di scussed. The study reveals that pH has a considerable effect on molar extinction coefficient values. These values are however not influenced by such additives like cetyltrimethyl ammonium bromide (CTAB). various strengths of carbonate-bicarbonate buffer and pota­ssium bromide at the same pH.