This paper presents how the OCM-G monitoring system together with the G-PM performance evaluation tool is used for observing and improving the performance of interactive grid applications. The OCM-G is an on-line grid-enabled monitoring system while the G-PM is an advanced graphical tool which enables to evaluate and present the results of performance monitoring, to support optimization of the application execution. The G-PM communicates with the OCM-G via OMIS. We show how how the application developer can analyze the performance of a real application using G-PM visualization.