Although the sequences of the ~13 500 genes of Drosophila melanogaster have been described, the functions of most of the encoded proteins are unknown. The classical genetic approach of starting with a mutation of interest followed by the subsequent molecular analysis of the corresponding gene have ascribed functions to only a small subset of the total number of genes. Large scale transposon mutagenesis screens and the isolation of a collection of lethal loss of function mutants has led to the assignment of vital functions for a larger fraction of the genes. However, many of the remaining genes appear to be infrequent targets of transposon insertions. Reverse genetic approaches such as gene targeting provide an alternative approach to generating loss of function mutations in a single gene, but are currently not practical for genome wide application. We are using RNA interference (RNAi) as a screening tool to identify new genes that are required for the development of the embryonic nervous system. Double stranded RNAs corresponding to ~1700 genes were synthesized in vitro and injected into preblastoderm embryos. After allowing the embryos to develop, the nervous system was visualized using mononclonal antibodies that stain subsets of neurons or axon tracts. Seventeen dsRNAs were identified whose injection resulted in a range of developmental abnormalities affecting the central and/or peripheral nervous system. Mutant phenotypes have not been described for most of the genes identified which included diverse classes of proteins including transcription factors, cell signalling components and enzymes. Mutants were also found in genes previously identified by classical genetic methods including members of the hedgehog signalling cascade, the anti-apoptotic gene, thread and the dynein light chain encoded by cut-up, and the transcription factor lola.