Seeking a potential explanation for why chaetocin-treated tumours were seemingly less vascular, and realising that phospho-VEGFR-1 level would be expected to represent a surrogate marker for the extent of VEGF activity in xenograft tumours, we examined tumour levels of both total and phospho-VEGFR-1 in homogenate of excised xenografts. The gene discussed is FLT1; the disease is neoplasm.