The hourly foraging activity of honey bees,Apis melliferaL., was observed on guayule,Parthenium argentatumGray, during two years, at Tucson, Ariz. Foraging activity occurred from 0700 to 1800 hours (MST) and the maximum abundance of pollen collecting was at 1000 hours. The percentage of guayule pollen collected by honey bees at Marana, Ariz., ranged from 2 to 76%. Pollen collections during the month of May had the highest amount and percentage of guayule pollen. Guayule plots with bees produced twice as much seed as plots from which bees were excluded. These results indicate that honey bees visit the guayule flowers, collect pollen, assist in pollination, and effectively increase quantity and quality of seed.