The purpose of this project was to investigate techniques that may be successfully applied to improve the characteristics of a bioprocess relevant mammalian cell line such as CHO (Chinese Hamster Ovary). The first technique explored in this thesis investigates the possibility of gene targeting and knockout using an AAV (adeno associated virus) viral vector. A custom vector was constructed comprised of an insertion cassette flanked by homologous ‘arm’ sequences generated from the region of genomic DNA being targeted. Infecting cells with this virus at an MOI of over 2 x 105 particles per cell, we have demonstrated that this unique genomic locus can be successfully targeted with foreign DNA through homologous recombination in CHO cells, with a targeting frequency of 3.1% calculated in this instance. While single allele knockouts were detected using a DHFR targeting vector, a number of alternative techniques implemented did not successfully isolate homozygous negative mutants, however further work based on the data provided in this study could successfully generate null mutants. The second technique applied is a variation of the directed evolution approach. A gene (TBP) was first selected that is known to be involved at a high level in the global cellular transcriptional machinery and subjected to random mutagenesis to generate a mutant library. When transfected this created a heterogeneous pool of diverse clones with a variety of phenotypes. An environmental stress was then applied for a number of passages to select for clones with suitable advantageous mutations, which were then isolated and characterised. Using this technique we successfully isolated a number of mutant clones with average maximum viable cell densities 53% greater than a control cell line when placed through the same stress selective procedure. This improvement in growth coupled with additional benefits to late culture stage viability contributed to an increase in accumulated integrated viable cell density (viable cell-hours) of over 44%. A transcriptional profiling experiment was also carried out to investigate the underlying cellular mechanisms that may have contributed to these advantageous metabolic changes.