The zebrafish (Danio rerio) is a potentially exquisite model system with which to investigate the genetic basis of cancer. But it has proved difficult to create stable transgenic lines of tumor-bearing fish. In the February 7 Science Langenau et al. report the generation of a zebrafish model of T-cell leukaemia that highlights the potential of using fish to find cures for cancer (Science 2003, 299:887-890). They created transgenic zebrafish expressing the mouse c-myc oncogene, or a fluorescent GFP-Myc fusion, under the control of the zebrafish Rag2 promoter. The fish developed tumors by the age of seven weeks. The fluorescence of GFP allowed monitoring of tumor formation and spread in the translucent fish. The clonal T-cell leukemias first appeared in the thymus and then spread to gills, fins and retro-orbital soft tissue. Langenau et al. also demonstrated the transplantability of the Myc-induced leukemias and found that the olfactory bulb is a preferred site for T-cell homing. The authors propose that the zebrafish cancer model offers promise for 'forward-gentics' screens to find modifier mutations and tumor suppressor genes, as well as large-scale drug screens for anti-cancer agents.