Populations of brewery Drosophila have been studied for 2 years. Species distributions diner between breweries, and are very different from those found in woodland and fruitmarkets. It is suggested that breweries form ‘urban islands’. One of the commonest species found in breweries appears to be Drosophila virilis, which has not previously been found in Britain. Tests on various characteristics, including courtship song, have shown conclusively that this species is a strain of D. virilis.