Cultivation of transgenic herbicide-resistant crops has become very attractive in the last 2-3 years. The potential risks and benefits on cultivation of such crops depend on the type of crop modification, herbicides to be used, but also of variable environmental conditions. Data on the use of herbicides on transgenic crops grown on a large scale are scarce. The safety of foods and animal feeding stuffs derived from transgenic crops is assessed through application of the concept of substantial equivalence. This process includes a thorough comparison of the composition of the modified foods with the proper traditionally grown product, a toxicological assessment of newly introduced gene products, and an evaluation of possibly unintended alterations. This information provides a solid basis for food and feed safety assessment.