Two integrating vectors developed for use in Saccharomyces cerevisiae were successfully employed for cloned gene integration in the yeast Kluyveromyces lactis. A delta-integrating vector carrying the dominant selection marker neo allowed tandem integrations of a CUP1(p)-lacZ cassette into one or two chromosomal sites. A delta/UB-integrating vector, which contains a reusable selection cassette, enabled multiple rounds of integration and the sequential insertion of stable, dispersed copies of CUP1(p)-lacZ. Subsequent gene expression was closely correlated with integrated copy number illustrating the promise of this method for metabolic engineering in K. lactis. While both vectors contain an S. cerevisiae delta target sequence, the presence of delta-like elements in K. lactis has not been confirmed. Given the degree of illegitimate recombination in this yeast species, the insertions likely occurred at random locations in the chromosomes.