To assess whether MD.45-HER/ζ cells had significant in vivo activity against HER-2/neu+ tumour cells, 1 × 106 murine ALC-HER lymphoma cells or an equal number of human FM3-HER-melanoma cells were inoculated s.c. in mice that had been irradiated (200 rad) 1 day before to suppress endogenous NK activity (Dorshkind et al, 1985; Lu et al, 1994). This evidence concerns the gene ERBB2 and lymphoma.