Imidacloprid and fipronil are two insecticides acting on the central nervous system. They are used worldwide, from the mid nineties, especially for seed coating of crops. Concomitantly to their introduction and their increasing use in French fields, honeybee populations decreased. Bee problems are nowadays reported in other countries (also called disappearing disease, desplobación de las colmenas, trouble des abeilles, deperimento degli apiari or colony collapse disorder). Bee problems have certainly several origins. Contamination of pollen and nectar by such chemicals appeared as one of the most probable cause, since subletal effects and chronic intoxications were observed on bees, at very low concentrations. We developed fully validated methods to measure contamination in pollen (sunflower and maize) for imidacloprid (HPLC/MS/MS) and for fipronil and 3 of its derivatives (GC/MS). For imidacloprid LOD and LOQ are 0.3 and 1 ng/g, respectively. For fipronil and each derivative (fiprole), LOD and LOQ are 0.07 and 0.2 ng/g, respectively. The averaged level of imidacloprid in pollen was 2-3 ng/g, which is 20-30 times higher than the concentration inducing significant mortality by chronic intoxication. Fiproles were detected in 48% of pollens issuing from treated crops. Fipronil and its sulfone derivative represented 77% and 17% of contaminants, respectively. The averaged fiprole sum Σf was 0.3 - 0.4 ng/g, which is 30-40 times higher than the concentration inducing significant mortality of bees by chronic intoxication.