We have investigated induction of vitellogenin and zr-proteins in rainbow trout (Oncorhynchus mykiss) liver and plasma, after in vivo treatment with estradiol-17b (E2) and alpha-zearalenol (a -ZEA). A method for quantification of zr-proteins and vitellogenin PCR products has been developed using oflourescent labeled probes (TaqMan assay). A partial sequence of rainbow trout zr-protein has been cloned (GenBank accession number AF185274) by alignment of available zr-protein sequences from four different fish species. The cloning was performed using reverse transcriptase polymerase chain reaction (RT-PCR) with an oligo dT primer followed by rapid amplification of cDNA ends (RACE) PCR and two degenerate zr-protein primers designed from a conserved region of the aligned sequences. This strategy resulted in a 700 bp long fragment that showed high amino acid sequence identity to that of salmon (77 %), winter flounder (64%), carp (63%) and medaka (61%) zr-proteins. For the in vivo experiment juvenile rainbow trout (50 - 100 g) were kept 10 fish per 370 liter tank at 15 °C (± 1) and acclimatized for 7 days prior to treatment, following a single intraperitoneal injection with E2 (0.01, 0.1, 1.0 or 10 mg/kg fish) or a -ZEA (0.1,1.0 or 10 mg/kg fish). Enzyme-linked immunosorbent assay (ELISA) showed induction for both proteins in blood plasma from fish treated with E2 or a -ZEA. The potency of a -ZEA was approximately 10-fold less when compared to E2. Furthermore, preliminary data using the TaqMan assay indicate a dose-dependent induction of vitellogenin and zr-proteins after treatment with E2 and a -ZEA.