The yeast synthetic lethal genetic interaction network contains rich information about underlying pathways and protein complexes as well as new genetic interactions yet to be discovered. We have developed a graph diffusion kernel as a unified framework for inferring complex/pathway membership analogous to "friends" and genetic interactions analogous to "enemies" from the genetic interaction network. When applied to the Saccharomyces cerevisiae synthetic lethal genetic interaction network, we can achieve a precision around 50% with 20% to 50% recall in the genome-wide prediction of new genetic interactions, supported by experimental validation. The kernels show significant improvement over previous best methods for predicting genetic interactions and protein co-complex membership from genetic interaction data.[Supplemental material is available online at www.genome.org.]Genetics establishes links between genotype and phenotype. Many genes are pleiotropic, carrying out multiple functions in different pathways under different environmental conditions and can have partially redundant function with other genes. Genetic buffering can be evolutionarily stable (Nowak et al. 1997). While individual gene perturbations may have little or no effect, combined perturbations can generate a phenotype. This is the rationale of genetic interaction screens, which test for phenotypes from two-gene perturbations that differ from the singlegene effects. Pairwise genetic interaction screens have been valuable in understanding functional relationships between genes and assigning functions to genes in a pathway-dependent manner.With the completion of the Yeast Knockout deletion collection (Giaever et al. 2002), high-throughput studies of pairwise lethal or growth defect interactions between null or hypomorph alleles of Saccharomyces cerevisiae (budding yeast) have made vast progress in the past few years. "Synthetic growth defect" or "synthetic sickness" describes a genetic interaction between two genes whose individual deletion mutants have minimal growth defects, while the double knockout results in a significant growth defect under a given condition. A subset of those pairs whose double knockouts lead to diminished growth or death are called "synthetic lethal" (Dobzhansky 1946). We will refer to the union of "synthetic sickness" and "synthetic lethal" as a "synthetic fitness or lethal interaction," or SFL. Multiple studies have screened a subset of deletions or hypomorph alleles against the entire set of viable yeast deletion mutants using methods including synthetic genetic array (SGA) (Tong et al. 2001, synthetic lethality analyzed by microarray (SLAM), and diploid-based SLAM (dSLAM) (Ooi et al. 2003;Pan et al. 2004Pan et al. , 2006. A second approach, termed an epistatic miniarray profile, searches for both positive and negative interactions among a subset of genes (Collins et al. 2007).Large . To achieve these goals, especially prediction of pathway membership, algorithms have progressed from counting the number of shared neighbo...