During the 1930's this type of research established some basic methods of observational studies and gathered basic data on social behavior, including aggression in young children. Human ethologists and observational research in child development in the 1970's have covered many of the same issues, using more sophisticated methodologies, statistical and analytic techniques, and theoretical interpretations. Research is considered ethological if it meets at least two of the following three criteria: 1) it relies mainly on direct, nonparticipant observation of behavior; 2) data is gathered in natural settings; and 3) the research focuses on the functional and comparative evolutionary significance of the behavior. These criteria can often be usefully combined with other approaches, although they are sometimes inappropriate. However, many researchers believe that behavioral research has placed insufficient emphasis on the use of direct, nonparticipant observation in natural settings. Figures, table, and 53 references.