This project studied the transcriptional response in larval fathead minnows to three different stressors, copper, zinc and heat. Differential display was used to identity stress-responsive genes in the genetically uncharacterized Pimephales promelas larvae. Two hundred and sixty-one clearly sequenced candidate bands were identified as being differentially expressed by copper, of which 148 were unique genes. One hundred and sixty-eight clearly sequenced candidate bands showed differential expression by zinc, 100 of which were unique genes. One hundred and sixty-seven heat-responsive differentially expressed bands were obtained, of which 107 were unique genes. Eight-five novel ESTs for the fathead minnow were homologous to functional genes from the NCBI database. In addition, this study identified 143 cDNAs homologous to genomic sequences of undetermined function within the NCBI database. Twenty-three dose-responsive genes that were identified in samples from two different stress experiments were quantified using an alternative more sensitive technique, real-time PCR. Gene expression was validated for two independent data sets from each of the stress experiments. Two genes, carboxypeptidase B and 60S ribosomal protein L12, were consistently repressed by copper in all gene assays. One gene, carboxypeptidase B, was consitently repressed by zinc in all gene assays of two independent experiments. One gene, fast muscle troponin I, was consistently repressed in response to thermal stress using samples from two independent experiments.