In order to assess the risks of transgenic crops for honey bee colonies, we studied the development of hypopharyngeal glands of adult workers. We introduced 50 newly emerged adult bees into small, queenright colonies of c. 250 bees. Bees were fed either Bt-transgenic maize pollen (MON 810) or a sugar solution containing either purified Bt-toxin (Cry1Ab, 0.0014% w/v) or Kunitz soybean trypsin inhibitor (SBTI) at two concentrations (0.1% and 1% w/v). Neither the Bt maize pollen nor the Bt toxin showed any effect on bee survival or on the development of hypopharyngeal glands after a period of 10 days' feeding. In contrast, treatment of newly emerged bees with SBTI (0.1 and 1%) for 10 days significantly reduced the mean weights of the hypopharyngeal glands and the mean diameter of the glands' acini. While small amounts of Bt toxin were detected by ELISA in the hypopharyngeal glands of bees fed the Bt-sugar solution, SBTI could not be detected in gland samples by Western blotting.