The purpose of this thesis was to develop a serum-free medium which would support the growth of a human tumour cell line, RPMI 2650. Serum is used almost universally as a medium supplement to support growth of cells in culture, but investigators in the field have long recognised the problems associated with the undefined, complex and variable composition of serum whereas serum-free media permit growth of cells in a precisely-defined environment. In order to gain experience in the techniques used to grow cells in culture in the absence of serum, initial work was carried out on a canine kidney cell line (MDCK), for which a serum-free medium had already been developed. Growth of RPMI 2650 was initially examined in reduced serum conditions at clonal cell densities and the effect of various growth factors, hormones and other nutritional factors was examined. Significant growth stimulation was observed due to the addition of a number of factors (transferrin, insulin, EGF and selenium). Growth occurred in dishes precoated with DEAE dextran in the absence of any serum supplement following addition of medium containing six components (transferrin, insulin, epidermal growth factor, selenium, ascorbic acid and a commerciallyavailable amino acid mixture, MEM non-essential amino acids).