Several different yeast species have been developed into systems for efficient heterologous gene expression. In this paper we review foreign gene expression in the dairy yeast Kluyveromyces lactis. This yeast presents several advantageous properties in comparison to other yeast species. These include its impressive secretory capacities, its excellent fermentation characteristics on large scale, its food grade status and the availability of both episomal and integrative expression vectors. Moreover, in contrast to the methylotrophic yeasts that are frequently used for the expression of foreign genes, K. lactis does not require explosion-proof fermentation equipment. Here, we present an overview of the available tools for heterologous gene expression in K. lactis (available promoters, vector systems, etc). Also, the production of prochymosin, human serum albumin and pancreatic phospholipase by K. lactis is discussed in more detail, and used to rate the achievements of K. lactis with respect to other micro-organisms in which these proteins have been produced.