For decades, organizations have used information technology (IT) to support their operational and managerial work. However, the use of IT varies considerably from one firm to another. Successful IT implementation occurs when IT is diffused to all organizational members and is used to the fullest potential (infusion). Prior studies tested several IT infusion enablers. However, they did not yield statistically significant results. These studies hypothesized IT diffusion enablers as IT infusion enablers. The lack of existing literature on IT infusion made theory-testing research rarely yield a reasonable result. In addition, the definitions and measures of IT infusion offered by existing literature are not validated. This study aims to identify factors that contribute to the different levels of IT infusion in the context of spreadsheet use in small audit firms and to offer a definition and measure of IT infusion. While prior studies have discussed several enablers of IT infusion, they have typically proposed enablers of IT diffusion rather than IT infusion. IT infusion is defined in this study as the use of IT to its fullest potential within a particular industry. Three aspects of infusion were identified in the prior literature. First, IT infusion refers to IT use within and across different business processes (extended use). For example, spreadsheets can be used to help auditors plan an audit, analyze data, and later create an audit report. Second, IT infusion refers to IT use in ways that establish the work-flow linkages within the work process (integrative use). For example, spreadsheets can be used to record data and the data is carried over for analysis and reporting. Third, IT infusion refers to IT use in tasks that could not be performed without IT (emergent use). For example, spreadsheets can be used to perform statistical analysis which cannot be done manually. The mixed methods research approach was chosen in order to provide a better understanding of the under-researched area of infusion. Use of theory-building approach from cases is likely to produce theory that is accurate and testable. Case studies are used for identifying IT enablers in real business settings. Quantitative data is collected using the survey questionnaire approach. In the first phase, a series of case studies were used to explore the concept of IT infusion in the audit context. All seven case firms were independent audit firms in Thailand with less than 100 employees. The firms helped identify a number of enablers of spreadsheet infusion. This study found infrastructure flexibility and training to be critical infusion enablers at an early implementation stage. At later stages, an IT champion, certain psychological factors, and social networks were found to be more important. The new measure was proven to incorporate all important IT infusion dimensions and to yield a reasonable range of scores enabling a complex statistical analysis. The study also used a questionnaire survey to gather data on spreadsheet infusion from 203 audit firms in Thailand. Partial least squares (PLS) regression was used to test a research model that was based on the earlier case studies. The analysis confirmed the relationships among IT infusion enablers and the three pathways of use which formed the concept of IT infusion. Task variety, an IT champion, and routinization were found to be directly related to IT infusion. Infrastructure flexibility, social networks, and management support were also found to contribute to IT infusion through other enablers. It is recommended that future studies use the concept of task complexity when examining IT infusion. In addition, future studies should extend investigations on psychological factors of individuals that may affect organizational IT infusion.