A proposed model of the sibling provision of social support in later life was tested using data from the Aging and Change in Rural Iowa pilot study, 1991-1992. The sample used in the present study consisted of 90 men and women over the age of 55 who were then living in one of three small towns in Iowa. The proposed model attempts to explain the likelihood of naming a sibling as a potential support provider in later life. The social support theories of Cantor, Litwak, and Bowlby are explored. Further, the model incorporates the elements of need, availability, and choice;Partial support for the model was found. For the unmarried aged, model independent variables of need, availability, and choice, together were found to explain a significant amount of the total variance in the dependent variable, as was parental status;The most striking finding was the infrequency of siblings named as potential support providers. 'Others' were named as potential sources of support about as often were adult children and more frequently than siblings.