When a structure is excited by fluid dynamic forces, direct measurement of such forces with transducers is often difficult because of the associated mounting problems. Consequently, an indirect estimation of these forces is useful. The indirect identification of fluid forces is based on: (i) measurement of the response on the structure under flow-induced excitation, (ii) an estimation of the modal parameters of the coupled fluid-structure system. In order to perform this modal identification, a digital signal processing method has been developed. This method, called Identification Modale Excitation Non Evaluee (IMENE), can be used to estimate modal parameters of a coupled fluid-structure system from structural response data without any excitation measurement. A time-domain multi degree-of-freedom parametric model is used, rather than the conventional isolated one degree-of-freedom model in the frequency domain. Because of the existence of finer structure inherent in the time-domain model used, the method can provide better resolution in identifying modal characteristics of the system. The indirect force identification method, called Methode d'Estimation Inverse des Excitations par Ecoulement (MEIDEE), can be used to estimate both fluidelastic and turbulence-induced forces. The first part of this paper deals with a general and concise theoretical presentation. In the second part the methodology is illustrated by a simple practical application: the cross-flow induced vibration of a single flexible cylinder in a rotated triangular array of rigid cylinders. The fluid dynamic forces applied on the flexible tube in the transverse direction have been estimated. These estimated fluid forces have then been used to compute a numerical solution of the tube transverse response. The agreement between the numerical solution and direct response measurements is very good, suggesting that the estimates of the fluid forces are reliable.