The Monsoon Trough Boundary Layer Experiment (MONTBLEX) is a multi-institutional, all-India coordinated program to study the atmospheric boundary-layer processes in the monsoon trough (MT) area of northern India. The experiment is being organized through a core program in which four observational towers are being set up in different meteorological regimes along the mean axis of the MT. The supplementary program will consist of two more meteorological towers at coastal stations over peninsular India. The pilot experiment conducted at the instrument tower during 1–7 July 1989 has shown the indigenous capability to design instruments with fast-measuring meteorological parameters, such as temperature, humidity, and wind vectors, through an on-site PC-based data-retrieval system. Similar tower-based instrumentation at three other sites—along with sodar, minisonde, tethered sonde, INSAT, radar and other observations—during the Monsoon 1990 experiment, will provide the requisite data for simulation and validation of planetary boundary layer models for the southwest monsoon. This paper presents the background, objectives, planning, and brief summary of the MONTBLEX pilot experiment.