Background: Pharmacist-physician collaboration may result in improved patient care. The model of collaborative working relationship (CWR) synthesizes such collaboration into 5 progressive stages, which are impacted by individual, context, and exchange characteristics; however, no study has demonstrated how to distinguish the 5 collaborative stages. Objective: Using CWR, the study objective was to identify factors associated with pharmacist-physician collaboration at baseline and at 3 months. Methods: This study consisted of 2 self-administered surveys mailed to a random sample of 750 Iowa pharmacists. The first survey assessed collaborative care at baseline and individual, context; and exchange characteristics. The second survey assessed collaborative care 3 months later. The measures for CWR constructs were modified from previously validated instruments. Individual characteristics; context characteristics, including practice setting, professional interaction, current collaboration status (yes/no); and exchange characteristics, including relationship initiation, trustworthiness, and role specification were obtained. Descriptive statistics, reliability analysis, and bivariate correlations were performed. Two regressions were conducted, wherein collaborative care at baseline and at 3 months were regressed over relationship initiation, trustworthiness, role specification, professional interaction, current collaboration, practice setting, and physician specialty, wherein the data for independent variables collected at baseline were used in both regression procedures. Results: Response rates were 33% (n = 239) and 79% (n = 188) for the first and second surveys, respectively. In the regression analyses, 85% and 35% of the variance in collaborative care at baseline and at 3 months, respectively, were explained. Trustworthiness and role specification were 2 predictors of collaborative care at baseline, and trustworthiness and professional interaction were 2 predictors of collaborative care at 3 months. Conclusions: Different factors were associated with collaborative care at different study times, which support a dynamic model of CWR. (C) 2010 Elsevier Inc. All rights reserved.