The measurement of the growth of colorectal hepatic metastases growth provides useful information for the management of patients, and can be used both as a prognostic variable and as an objective assessment of treatment efficacy. A number of techniques have been used to quantify such growth, including measuring the change of an anatomical measure such as tumour size or the percentage hepatic replacement. Cell kinetic studies and analysis of the changes in serum tumour markers such as carcinoembryonic antigen (CEA) are other methods. Anatomical measures are unlikely to be reliable because within the liver a metastasis may change in volume as a consequence of non-neoplastic factors outside the liver. It may also be incorrect to assume that the changes observed in an abnormality identified by radiological methods are the direct result of a change in the neoplastic burden. Measurements of cell kinetics and serum tumour markers are complicated by neoplastic cell heterogeneity across the tumour and are subject to sampling errors. All techniques presently available therefore can be considered to be indirect measures and may not be truly representative of tumour growth. These limitations of growth measurements have to be recognised when applied to the assessment of tumour response.