Experiments were performed to elucidate resistance of perennial glandular-haired alfalfa to the potato leafhopper, Empoasca fabae (Harris). The primary objective was to determine if the resistance factor was associated with the glandular trichomes or if toxins were present in the plant phloem. It was also of interest to examine if stem lignification hampered/prevented feeding. Plant resistance was initially verified using free-choice experiments, which compared leafhopper feeding injury between the resistant glandular-haired alfalfa clone FGplh13 and the susceptible alfalfa variety P5373. The resistant clone FGplh13 was determined to express significantly lower levels of injury. The same plant treatments were also used in no-choice tests with 1^st and 3^rd instar potato leafhoppers. Significantly higher levels of leafhopper mortality were associated with the resistant glandular-haired clone. In fact, no 1^st or 3^rd instars survived on FGplh13 after 48 h. Additional no-choice experiments were performed using FGplh13 alfalfa with the glandular and nonglandular trichomes intact and removed, along with the susceptible alfalfa variety P5373 with the nonglandular trichomes intact and removed. Following removal of the glandular trichomes from FGplh13 alfalfa, mortality of nymphs and adults significantly decreased. In all instances, significant differences in nymphal and adult mortality were not detected between FGplh13 (removed) and P5373 (intact and removed) alfalfas. In addition, no significant differences were detected in the developmental time for the potato leafhopper from 1^st to 3^rd instar, 3^rdto 5^th instar, and 5^th instar to adult between FGplh13 (removed) and P5373 (intact and removed). First (and possibly 2^nd) instars were also observed to be entrapped by the glandular trichomes found on FGplh13. Comparisons of stem lignification, total number of vascular bundles, and stem diameter between FGplh13 and P5373 alfalfas did not reveal any significant differences. Examination of the behavior of 1^st and 3^rd instars noted a significant increase in cleaning of tarsi, changing in feeding location, restlessness while stylets were inserted, and jumping/falling off the plant surface on the resistant FGplh13 alfalfa. The glandular hairs were also found to significantly interfere with the general movement of 1^st and 3^rd instars, as evidenced by the time required to travel a specified distance on the resistant FGplh13 and susceptible P5373 alfalfas. Additional no-choice experiments found adults to settle less frequently on FGplh13 alfalfa, along with exhibiting increased restlessness. Two-way choice tests examining nonpreference of adults found that P5373 (intact) alfalfa and FGplh13 (removed) alfalfa were significantly preferred over FGplh13 (intact) alfalfa. Overall, the glandular trichomes appear to be providing the major resistance factor, which is partly expressed via a tactile component. Our results did not indicate that toxins were present in the plant phloem or that stem lignification prevented/hampered feeding. Resistance to adults is chemically based, while resistance to nymphs is chemically and mechanically based.