The cash balances of businesses have recently become one of the main topics of interest in the financial area. As a result of this interest, several studies and theories have been applied to this field, mainly to larger companies, and with a lesser application to the universe of small businesses. Portuguese business context is mainly composed by owner managed companies of the small businesses. The theoretical support that was considered most appropriate to back the analysis was the trade-off theory. The trade-off theory, in general terms, explains the amount of cash reported by companies on their balance sheets. This study is based on a sample of Portuguese manufacturing firms. It uses a methodology of econometric nature, based on models that were constructed to test if the tradeoff theory can explain the amount of cash held by these companies. The modeling considered four key variables (determinants) significant in the explanation of such amounts: the "net working capital", the "debt", the "size" and "cash flow". Moreover, after a closer analysis, the results indicate that there are significant differences when if there is or not an auditor that certifies the accounts of the companies is added as control.