A 215 kDa molecule termed T19 marks CD4-CD8- T cells in sheep and cattle. In this report, we analysed the T19 or "null cell" panel of mAbs against γδT cells of sheep, using a mAb specific for the γδTCR. By two-colour immunoflourescence, all of the mAbs in the T19 panel reacted with γδT cells or subsets thereof, although staining intensities and percentages of cells stained by the different mAbs indicated considerable heterogeneity for the T19 molecule. This probably results from differential expression of certain epitopes on T19. The reactivity of most of the mAbs ffor the 215 kDa T19 molecule was also confirmed by immunoprecipitation and SDS-PAGE.