The inference of regulatory and biochemical networks from largescale genomics data is a basic problem in molecular biology. The goal is to generate testable hypotheses of gene-to-gene influences and subsequently to design bench experiments to confirm these network predictions. Coexpression of genes in large-scale geneexpression data implies coregulation and potential gene-gene interactions, but provide little information about the direction of influences. Here, we use both time-series data and genetics data to infer directionality of edges in regulatory networks: time-series data contain information about the chronological order of regulatory events and genetics data allow us to map DNA variations to variations at the RNA level. We generate microarray data measuring time-dependent gene-expression levels in 95 genotyped yeast segregants subjected to a drug perturbation. We develop a Bayesian model averaging regression algorithm that incorporates external information from diverse data types to infer regulatory networks from the time-series and genetics data. Our algorithm is capable of generating feedback loops. We show that our inferred network recovers existing and novel regulatory relationships. Following network construction, we generate independent microarray data on selected deletion mutants to prospectively test network predictions. We demonstrate the potential of our network to discover de novo transcription-factor binding sites. Applying our construction method to previously published data demonstrates that our method is competitive with leading network construction algorithms in the literature.L arge-scale sequencing has provided a wealth of data on the presence, absence, and variation of genes within and between species. However, functional annotation is unavailable for many genes and the majority of genes within most species are not placed within regulatory or biochemical pathways. Classic biochemical methods for placing genes in pathways cannot keep pace with the rapidly increasing amount of genomic information. To address this problem, we and others have been developing methods to infer networks from large-scale functional genomics data (1-5). The overall goals of such methods are to generate predictions of systems behavior and testable hypotheses of gene-to-gene influences. Predictions of systems behavior can be useful even in the absence of detailed mechanistic understanding. For example, the predicted response to the inhibition of a given gene can guide the selection of drug targets (6). The generation of testable hypotheses provides a path to more rapidly gain mechanistic understanding as it focuses bench experiments on subsets of potential gene-to-gene influences. Moreover, network construction and experimental work can be used in an iterative process to converge on underlying mechanisms (7,8).At present, the data most used in network construction methods are from large-scale gene-expression studies. Coexpression of genes across a wide variety of experimental conditions implies coregulation (9, ...