Endotrophic mycorrhiza in tomato and maize, induced by chlamydosporic varieties of Endogone macrocarpa, were examined quantitatively by estimating infection of roots, pigmentation of roots and production of ectocarpic chlamydospores. When the size of the root system was taken into account, estimates of infection showed a relationship to growth of the host. The amount of pigmentation within the root system gave a good indication of mycorrhizal intensity and was related to the size of the host at high levels of infection. The numbers of spores produced on an individual root system, given a particular treatment, were positively correlated with the size of the host. The relative merits of these different assessments of mycorrhiza are discussed.