We have produced a functional murine antibody to dioxin in the culture medium of the methylotrophic yeast Pichia pastoris. Complementary DNA copies encoding the light (kappa) and heavy (gamma) chains of the dioxin monoclonal antibody, DD1, were each placed under the control of P. pastoris alcohol oxidase (AOX1) promoter and Saccharomyces cerevisiae alpha-mating factor secretion signal sequence. The resulting expression cassettes were assembled into a single plasmid (pPICZ alpha DD1) to permit co-expression of both light and heavy chains of the antibody molecule. P. pastoris SMD1168 (pep4, his4) transformed with pPICZ alpha DD1 was able to secrete intact antibody into the culture medium. As high as 36 mg l(-1) of the antibody was produced in shake-flask cultures after 96-h induction with methanol. Functional analysis using immunoassay confirmed murine nature of the recombinant antibody and its ability to bind dioxin.