SUMMARYThe visitation rate of honeybees on alfalfa may possibly be measured by determining the sugar concentration of nectar in the honey stomachs of foraging bees. This concentration is shown to be largely controlled by the relative humidity and the time available for nectar evaporation in the alfalfa blossom, which in turn depends on the rate of visitation by honeybees. An adjustment for relative humidity may be necessary in order to compare readings widely separated in time or location. Where conditions are relatively constant from day to day, it may be sufficient to measure the nectar sugar concentration and relative humidity at the same hour each day. In one experiment a highly significant correlation coefficient of−0·867 was obtained between the number of tripped flowers per raceme and the nectar sugar concentration; in another experiment a non-significant value was obtained.