In this paper, we use the Furfine (1999) statistical procedure to identify money market operations from Payments Systems data. Given the availability of an alternative data set, recording money market operations we could confirm the accuracy of the method. We examine evidence on integration of the money market in the euro area. We ask: “how do Portuguese banks participate in the market for daily funds?” and look for a possible hierarchical structure in the market. We find strong evidence of integration and mixed evidence on hierarchical structure.