Composing often involves such operations as addition, reordering, substitution and embedding (Emig, 1971; Tse, 1984). On any occasion when one's original intentions `in the head' have to be altered to accommodate the demands of writing, one can say that a transformation has had to be made. To throw light on this usually hidden processing as it applies to writing, the subjects (Hong Kong students) in the present study were asked to compose aloud in Cantonese (a spoken language), their efforts being interpreted as indications of the intended representations for inclusion in their written output. The researcher then examined the differences between the `compose aloud' productions and the representations eventually written down on paper (Modern Standard Written Chinese), any discrepancy between the two being judged a potential `transformation'. Discrepancies between the subject's intentions and what was actually produced can help indicate the production difficulties encountered and the strategies used by subjects. Most importantly for this study, they also reflect the subject's facility with the languages used. It is found that transformation is a very significant process in composing among Chinese students in Hong Kong.