Preference among, and relative consumption and use of several legumes by third instars of the cabbage looper,Trichoplusia ni(Hübner)(Lepidoptera: Noctuidae), were studied under laboratory conditions. Leaf disks of the relatively insect-resistant ‘PI 227687’ and insect-susceptible ‘Davis’ soybean,Glycine max(L.) Merrill; and of snap bean,Phaseolus vulgarisL.; and ‘Henderson's Bush’ lima bean,P. lunatusL. were preferred to sucrose-treated elderberry-pith disks; thus, the phagoexcitant effects of primary and secondary substances from the leaves of all plants exceeded those of sucrose alone. Leaf disks of ‘PI 227687’ were significantly less preferred than those of ‘Davis’ soybean and lima bean. Consumption and utilization of ‘Henderson's Bush’ lima bean and ‘Davis’ soybean leaves were most efficient, and of ‘PI 227687’ soybean leaves were least efficient. A lower rate of food intake on snap bean was associated with a higher efficiency of conversion of ingested food into body matter. Efficiency of conversion of digested food (ECD) into body matter was significantly and positively associated with the growth rate (GR) of larvae on the most suitable host plant, lima bean, but was negatively associated in larvae on ‘PI 227687’, the least suitable host. The relatively high consumption index (CI) on ‘PI 227687’ indicated significant antibiotic effects from secondary substances in ‘PI 227687’. Relative preference observed in leaf disk assays was not reflected in host-plant suitability based on consumption and utilization of foods. To understand better the insect-plant interrelationships, both insect preference for, and consumption and utilization as food should be studied.