Reissue of the PA-18-399. The purpose of this Funding Opportunity Announcement (FOA) is to encourage research grant applications to support research designed to elucidate the etiology, epidemiology, diagnosis, and optimal means of service delivery in relation to Autism Spectrum Disorders (ASD). An R03 grant supports small, discrete, well-defined projects that can be completed in two years and that require limited resources. An R03 grant application may not contain extensive detail or discussion. R03 applications may include development of new research methodologies or technology, secondary analysis of existing data, and pilot or feasibility studies. Preliminary data are not required, particularly in applications proposing pilot or feasibility studies.