The mining sector and the industrial sector each comprise a significant proportion of the total market capitalisation of The Johannesburg Stock Exchange. The factors affecting the fortunes of these two sectors can be quite different over extended periods of time and this should be taken into account in “market model” analyses of share price behaviour. This is quite easily done via multiple regression analysis. Although portfolio analysis based on the resulting share risk parameters is slightly more complicated than that conventionally performed, its results are intuitively acceptable and perhaps of greater value in practical applications.