The neuroendocrine-differentiated colonic carcinoma cell line (LCC-18) was transplanted to 29 nude mice (Balb/c). The purpose of the present study was to establish an animal model that would allow monitoring with magnetic resonance imaging (MRI) of changes induced by interferon (IFN) therapy and to evaluate whether the therapeutic response, as expressed by changes in MR signal characteristics and tumour proliferation activity, could be modulated by different IFN dosages. IFN did not seem to have any obvious antiproliferative effect on the LCC-18 tumour cell line transplanted to nude mice and no convincing treatment-related changes in rho values or T1 and T2 relaxation values were observed. The animal model was probably unsuitable for demonstration of IFN effects.