GAL4 is a yeast regulatory protein that binds to specific sites within a DNA sequence called UASG (galactose upstream activating sequence) and activates transcription of linked genes. This activation requires two functions of the protein: a DNA binding domain located near the amino terminus, and one or more 'activating regions'. The 'activating regions' are highly acidic (see also ref. 12) and can be replaced, for example, by a short peptide designed to form a negatively charged, amphipathic alpha-helix. GAL4, as well as deletion derivatives bearing one or more 'activating regions' attached to the DNA binding domain, activates transcription in cultured mammalian cells from mammalian promoters linked to a UASG (refs 14, 15). Here we show that GAL4, when expressed in particular tissues of Drosophila larvae, stimulates tissue-specific transcription of a Drosophila promoter linked to GAL4 binding sites.