To assess potential impacts of transgenic pest-resistant plants, newly-emerged adult honey bees from ten colonies were tagged, placed in cages at 33 oC, and fed with 625 ìg/g Cry1Ba Bacillus thuringiensis (Bt) toxin or 2.5 mg/g aprotinin proteinase inhibitor in pollen-food (equivalent to 0.25% or 1% of total soluble protein). Control bees were given similar food without additive. All foods were consumed at similar rates. After seven days, all bees were returned to their hives. Subsequent observations showed that Cry1Ba-fed bees did not differ significantly from control bees in the timing of their first flight, the period during which flights took place or in estimated longevity. However, aprotinin-fed bees began to fly and also died about three days sooner than Cry1Ba-fed or control bees. Their flight periods were similar to those of the other bees. The effects of transgenic aprotinin-plants on honey bees will thus depend on gene expression levels in pollen.