In previous research, participation in science studies in senior secondary school has been related to both background characteristics of students and to earlier achievements and interests. This paper reports an investigation of participation in combinations of subjects in senior secondary schools in Australia which embody different science orientations. It shows that different combinations of factors shape participation in physical science' and 'biological and other science' types of course. Both are favoured by investigative interest but participation in a physical science course type is strongly associated with high levels of earlier school achievement in numeracy and gender whereas participation in a biological and other science course type is more strongly associated with social background and curriculum influences. In addition the paper suggests that the low participation by females in physical science courses should be interpreted in terms of an interactive influence of gender, earlier achievement and socio-economic background.