The health effects of a Roundup-tolerant NK603 genetically modified (GM) maize(from 11% in the diet), cultivated with or without Roundup application and Roundupalone (from 0.1 ppb of the full pesticide containing glyphosate and adjuvants) indrinking water, were evaluated for 2 years in rats. This study constitutes afollow-up investigation of a 90-day feeding study conducted by Monsanto in orderto obtain commercial release of this GMO, employing the same rat strain andanalyzing biochemical parameters on the same number of animals per group as ourinvestigation. Our research represents the first chronic study on thesesubstances, in which all observations including tumors are reportedchronologically. Thus, it was not designed as a carcinogenicity study. We reportthe major findings with 34 organs observed and 56 parameters analyzed at 11 timepoints for most organs. Biochemical analyses confirmed very significant chronic kidney deficiencies, forall treatments and both sexes; 76% of the altered parameters were kidney-related.In treated males, liver congestions and necrosis were 2.5 to 5.5 times higher.Marked and severe nephropathies were also generally 1.3 to 2.3 times greater. Infemales, all treatment groups showed a two- to threefold increase in mortality,and deaths were earlier. This difference was also evident in three male groups fedwith GM maize. All results were hormone- and sex-dependent, and the pathologicalprofiles were comparable. Females developed large mammary tumors more frequentlyand before controls; the pituitary was the second most disabled organ; the sexhormonal balance was modified by consumption of GM maize and Roundup treatments.Males presented up to four times more large palpable tumors starting 600 daysearlier than in the control group, in which only one tumor was noted. Theseresults may be explained by not only the non-linear endocrine-disrupting effectsof Roundup but also by the overexpression of the EPSPS transgene or othermutational effects in the GM maize and their metabolic consequences. Our findings imply that long-term (2 year) feeding trials need to be conducted tothoroughly evaluate the safety of GM foods and pesticides in their full commercialformulations.