The purpose of this article is to report an experiment performed with an Acoustic Doppler Current Profiler-ADCP, under tropical environmental conditions, aimed at testing and evaluating the ADCP and comparing the results obtained with those provided by traditional methods used in the Amazon River Basin. The HiBAm research team tested the ADCP over a 4-day period at the Manacapuru section on the Solimões River. During this period, 34 water discharge measurements were completed, whereas only a maximum of only 3 measurements would have been possible using traditional methods, due to operational limitations. The ADCP results differed from the other methods by about 9%. However, the final water discharge results (93 × 103 m3.s-1 for the experiment period) showed that the ADCP offers fundamental advantages in terms of measurement reproducibility (less than 1%), speed (only 30 min for a 3000-m transect), reduced number of people (two) and safety. The results also indicate that the ADCP can help solve the problem of scatter associated with the rating curve for Manacapuru. Copyright © 2009 John Wiley & Sons, Ltd.