Problems concerning conceptual change from existing knowledge (accumulated from everyday experiences or earlier teaching) to new scientific knowledge concerning natural phenomena are fundamentally the same for Western and non-Western students. However, difficulties experienced by non-Western students are magnified by factors such as their cultural experiences, beliefs, and language structure. In this study an attempt was made to analyze and represent the knowledge structures of a group of non-Western students from Qwa Qwa, South Africa (N=40) and to compare these structures with those involved in the orthodox scientific version of density. The study includes a description of the use made of these knowledge structures by selected students in solving the problem of why some objects float and others sink in water. Results indicate that few students' answers involved the Western scientific definition of density and that many answered in terms of alternative conceptions of mass, volume, density, and force. These and other results have implications for teaching Western science to students in a non-Western culture. They also have similar implications for science teaching within Western cultures where students acquire alternative conceptions which are a consequence of everyday experiences and which conflict with the orthodox scientific conceptions presented to them in school. (JN)