Twenty transgenic Carica papaya plants ('Sunset', Roclone 55-l) carrying the coat protein gene (cp) of papaya ringspot virus (PRV) strain HA 5-l have remained symptomless and ELISA-negative for 18 mo. after inoculation with Hawaiian PRV under field conditions. Control plants showed disease symptoms within 1 mo. after manual inoculation or within 4 mo. when aphid populations were the inoculum vectors. Trunk diameter was significantly greater in cp + plants (14.3 cm) than in PRV-infected controls (9.3 cm). Fruit brix, plant morphology, and fertility of cp + plants were all norm al. Segregation analysis in R1 seedlings indicated that 55-1 contains a single transgenic insertion site. PRV resistance in R1 plants was linked with the cp gene, although in some progenies, up to 50% of cp + plants developed mild PRV symptoms more than 3 mo. after inoculation. Preliminary tests suggest that this is not due to genesis of virulent mutant strains of PRV.