Using a gel mobility shift assay, protein factors have been identified that may participate in the transcriptional regulation of the juvenile hormone (JH) induced vitellogenin A (VgA) gene of the migratory locust. Two DNA-binding proteins were found that were modulated in correlation with VgA gene activity during normal reproductive cycles and experimental stimulation by an active JH analogue (pyriproxyfen). One of these, JH factor (JHF), may be a regulator of VgA and perhaps other JH-responsive genes. The second, mobile factor (MF), appears to have a more general role in cellular responses to external stimuli such as JH and wounding. JHF and MF may represent factors that act together with the JH receptor to regulate VgA gene transcription.