Questions have been raised about Séralini’s study protocol. But Séralini designed his study to be comparable with Monsanto’s[1] – thus the design was similar. While the Monsanto study used twice the sample size (rats per group) as Séralini, the Monsanto authors only analyzed blood and urine from half of the animals – the same number of sampled animals as in Séralini’s study. Both studies used the same rat strain – the Sprague-Dawley.

Séralini added elements that made his study more detailed than Monsanto’s. He tested three levels of GM maize exposure, compared with Monsanto’s two, and measured a larger number of effects more often. Furthermore, Séralini added additional treatment groups, namely NK603 maize not treated with Roundup, and Roundup exposure alone (in drinking water). This was done in an effort to ascertain whether any ill effects observed were due to the GMO, Roundup or a combination of the two. Again, this is an issue that industry and regulators have failed to address. 

The key difference between the studies was thus not in research protocol, but in breadth of analysis and study duration. Crucially, Séralini’s study lasted two years, as compared with Monsanto’s 90 days. This proved to be important because in Séralini’s study, the first tumours only became visible four months into the experiment – a month after Monsanto’s study had ended.

According to the OECD protocol for chronic toxicity studies like Séralini’s, it is acceptable to extend such a study to two years if scientifically justified. The unexpected tumour observations, beginning in the 4th month, could be considered to provide justification to extend the study length.[2]

Both studies were reviewed, accepted, and published by the same journal – Food and Chemical Toxicology (FCT). Only Séralini’s paper has been retracted.


[1] Hammond B et al (2004). Results of a 13 week safety assurance study with rats fed grain from glyphosate tolerant corn. Food Chem Toxicol 42(6): 1003-1014.

[2] Organisation for Economic Cooperation and Development (OECD) (2009). OECD guideline no. 452 for the testing of chemicals: Chronic toxicity studies: Adopted 7 September 2009.