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Empirical observations generally indicate a shifting and decreased <i>Lolium</i> spp. susceptibility to glyphosate in Italy. This is likely due to the long history of glyphosate use and to the sub-lethal doses commonly used. There is, therefore, a need to determine the variability of response of <i>Lolium</i> spp. to glyphosate and identify the optimum field dose. To perform a sensitivity analysis on <i>Lolium</i> spp. populations in an agriculture area, collection sites were mainly chosen where glyphosate had not been applied intensely. Known glyphosate-resistant or in-shifting populations were included. Two outdoor dose-response pot experiments, including eleven doses of glyphosate, were conducted. The dose to control at least 93%&#8722;95% of susceptible <i>Lolium</i> spp. was around 450 g a.e. ha^&#8722;1. However, to preserve its efficacy in the long term, it would be desirable not to have survivors, and this was reached at a glyphosate dose of 560 &#177; 88 g a.e. ha^&#8722;1. Taking into account the variability of response among populations, it was established that the optimal dose of glyphosate to control <i>Lolium</i> spp. in Italy up to the stage BBCH 21 has to be at least 700 g a.e. ha^&#8722;1. As a consequence, it is recommended to increase the label recommended field rate for <i>Lolium</i> spp. control in Italy to a minimum of 720 g a.e. ha^&#8722;1.