The external P requirements of yams ranged from 0·005 to 0·02 p.p.m. P in solution. D. alata had the highest P requirement but also gave the highest yields. D. esculenta and D. rotundata which produced lower yield did not respond to applied P. There appeared to be a relationship between yield potential and the external P requirement. Internal P concentration was not a good indicator of whether or not the yields of D. alata and D. esculenta would respond to applied P. All three species of yam efficiently utilized P at low concentrations in the soil solution. Yams appear to depend on an effective mycorrhizal association to meet their P requirement.