We consider LISA observations of in-spiral signals emitted by massive black
hole binary systems in circular orbit and with negligible spins. We study the
accuracy with which the source parameters can be extracted from the data
stream. We show that the use of waveforms retaining post-Newtonian corrections
not only to the phase but also the amplitude can drastically improve the
estimation of some parameters.Comment: Latex 2 pages, 1 figure. To appear in: "Third Amaldi Conference on
Gravitational Waves". Edt. S. Meshkov; American Institute of Physic
