the poliacrylamide gel electrophoresis sodium dodecylsulfate (page-sds) has been extensively used to separate native and denaturalized proteins. in various countries this has been useful to detect milk adulteration with whey, which is a fraud according to the current legal standards. the presence of glicomacropeptide (gmp) constitutes a marker of adulteration. it is released to the serum due to the hydrolysis of k-casein peptide catalyzed by rennin incheese elaboration. in this work, the gmp detection was standardized as a pasteurized milk adulteration index, by means of gmp isolation with sequential precipitation in trichloroacetic acid at 24% and 50%, treatment with ethanol-ether and resuspention in buffer tris-hcl 0.05 m, edta 1 mm, ph 7.2 from sweet whey, acid whey, recently drawn raw milk, mixtures of whey: milk; pasteurized milk and powder milk locally commercialized. precipitates were analyzed by sds-page and gmp was evidenced as a trimer of 20.8 kda in samples of sweet whey, and mixtures of whey: milk (1, 5, 10 and 50%), but absent in samples of acid whey and drawn raw milk. analysis of fifteen samples of pasteurized milk (brands a, b, c, d and e) revealed the presence of gmp in ten of them, corresponding to brands a, b, c and e. nevertheless after analyzing five samples of powder milk (brands f, g, h, i y k) this peptide was not observed. the results obtained demonstrate that investigation of gmp by sds-page in milk, constitute a sensible and specific parameter to detect milk adulteration with whey, to levels as low as 1%, something that can not be revealed only with the evaluation of the physical-chemical parameters of milk.