The objective of this research was to study the regulation of stomatal opening in beans, and to find whether it is caused by a decrease in the leaves’ water potential, or by a chemical factor in the roots. An experiment was carried out during 1997 in Montecillo, Mexico with the Cacahuate 72 variety, type I Nueva Granada breed. The experiment took place in a controlled environment chamber where plants had their roots split into two parts. Two irrigation treatments were applied twenty-seven days after sowing: a) irrigation, and b) irrigation/irrigation interruption. A system was created with 9-cm diameter and 50-cm high PVC tubes, divided vertically. Treatments lasted 15 days, and stomatal conductivity, hydric relations (water potential, osmotic potential, and turgid pressure), and proline content were quantified on a daily basis. Plants undergoing water stress showed a decrease in conductivity and a slight increase in proline content, and these plants did not show differences in hydric relations as compared to the ones undergoing irrigation. Results suggested that there is non-hydraulic communication between roots under water stress, and leaves under the same condition.