Deltamethrin Decis® is a synthetic pyrethroid recently put on the market ; like any pyrethroid, deltamethrin is used at very low concentrations (5 g/ha used against pollen beetle on oilseed rape) and appears to have a repellent effect on honey bees. The repellent effect of the adjuvants in the deltamethrin formulation was quantified precisely either in a flying cage or in a glass house. A " field test " on a 30 ha oilseed rape plot with three bee-yards led us to conclude that deltamethrin presents a very low hazard to honey bees, under the usual conditions of treatment - at least, in the short term. This concrete instance gives us a new opportunity to stress the fact that the poisoning mechanisms and olfactive perception of a repellent substance are linked to the experimental environment ; the final interpretation of such mechanisms depends on a large spectrum of complementary approaches.