The goal of this study was to evaluate the presence Cry toxin in milk of cows feeding transgenic maize hybrids. Twenty-four Jersey cows were allotted into 2 groups: control (n = 12), feeding conventional diet, or test, consuming grain and silage from maize with cry gene from Bacillus thuringiensis (n = 12). A paired t-test was used to determine whether there were significant differences between the 2 treatments. Were used 0.5 g of maize leaves transgenic lyophilized, macerated in liquid nitrogen, resuspended in 1 mL of methanol (80%) and diluted with 4 mL of PBS buffer as immunoassay antigen. Two female New Zealand rabbits were used to produce polyclonal antibodies against Cry1A105, Cry2Ab2, Cry1F, Cry1Ab and VP3Aa20 toxins from DKB 390 VT Pro II, AG 8088 Pro II, Biomatrix 2B655 Hx, Syngenta Impacto TL TG and Syngenta 7205 Viptera, respectively, to be used as a screening for maize-derived food products, by plate-trapped antigen (PTA)-ELISA. Immunogen was prepared bioconjugating Cry toxin to carbodiimides. Immunizations were performed each 15 d. At the end of 5 immunizations the rabbits were bled and sera were kept at –80°C. Antibodies were purified in immunoaffinity columns between 50 and 100 kDa. Milk samples, collected 3 time each 14 d during 56 d, were frozen and lyophilized. Antigen (100 μL) were placed into micro wells in triplicates and incubated 1 h at 37°C. Blocking were done using 200 μL of PBS buffer added to 1% BSA for 1 h 37°C. Plates were dried and 100 μL of anti-sera dilution (1:500) were placed, for 1 h at 37°C. Plates were washed (PBS) and anti-rabbit conjugated HRP sera dilution (1:1000) was added. After 1 h at 37°C, plates were washed (PBS-T-G) and PNPP (p-nitrophenyl phosphate) revealed, at 450 nm. The presence Cry toxin analysis did not differ between milk of cows fed by transgenic maize hybrids and its nonbiotech counterpart. Results showed that the milk system production using silage and ration with transgenic maize hybrids that contains cry gene is safe and the antibodies produced through leaves as antigen are highly sensitive and specific to Cry toxin and can be used on an enzyme immunosorbent with low cost, high sensibility and specificity.