This thesis analyses the effects of relative market share and the rate of market growth on the strategic characteristics and financial performance of selected companies quoted on the Johannesburg Stock Exchange over the period 1977 to 198. It is well established that business performance is partially contingent upon relative market share position and the rate of market growth. Together these variables comprise the basis of the Boston Consulting Group approach to portfolio analysis in the form of the Boston Consulting Group Growth/Share Matrix. A methodology was designed to test the validity of this matrix in measuring and predicting corporate behaviour at the business level in South Africa. Selected companies were placed into the matrix and analysed in terms of their strategic attributes (represented by selected financial ratios) and their level of performance (represented by a wide range of financial performance measures). The research findings show that relative market share and the rate of market growth have a significant impact on the strategic attributes and financial performance of South African businesses. Also, certain attributes are closely associated with particular types of performance. Therefore, given a specific performance target, management should ultimately be able to isolate and monitor the relevant strategic attributes in ensuring that the target is achieved. The analysis of contingent models of strategy is still in its infancy, but this study indicates that the field is possessed of great potential.