The marked increase in demand for contraceptives and anti-inflammatory agents such as cortisol and prednisolone, combined with a diminishing supply of steroid raw materials may lead to shortages of steroid drugs1. Thus it is important to develop new sources for steroids as well as to devise more efficient means for steroid conversions. Here we report a new approach to steroid transformation in which activated immobilised microorganisms are utilised and which represents a promising alternative to conventional microbial transformation processes.