Summary A step-wise practice procedure developed for conducting behavioral assessment and modification with individuals and families in open community settings was applied with a sample of 32 cases. These cases embraced 66 problem areas characteristic of the diverse behavioral difficulties encountered in open service settings. Eight practitioners working under close supervision employed the Procedure for a period of 8 months in two family service agencies. It was found that the Procedure provided for orderly and systematic behavior modification for the large variety of cases that may be encountered in the open setting and other services and occasional crises could be managed with only temporary delay in orderly progress in behavioral modification. There was a high degree of effectiveness for problems progressing to the point of modification or to maintenance. Although some countervailing conditions were found which interfered with case activity, these influences were rarely a serious threat to behavior modification. Positive changes in contracted behavior were not accompanied by an increase in negative changes in non-targeted behavior and there were more positive than negative changes in non-targeted behaviors incidental to work on targeted behavior. The most important potential threats to successful behavior modification in the open community setting were attrition (27 per cent premature termination) and client inaccessability. These areas should be addressed in future work on behavioral procedures for community settings. In addition to several procedural guidelines of the type applied here, behavior modification in the open setting also requires specialized procedures for purposes of handling such particular difficulties as family communication and decision making, as well as life situations involving crises and temporary and transitional status.