Sixty plants in each of 27 fields of hop (Humulus lupulusL.), mostly of the locally bred triploid cultivars ‘Superalpha’, ‘Greenbullet’, and ‘Sticklebract’ were tested for viruses by enzyme-linked immunosorbent assay (ELISA) in 1984. Fifteen of the 24 fields containingPrunusnecrotic ringspot virus (NRSV) had incidences of >81%. Both the intermediate (I) and apple (A) serotypes of NRSV were detected. Seventeen of 24 fields with arabis mosaic virus (ArMV-H) had incidences of <41%. Twelve of 22 fields containing hop mosaic virus (HMV), 13 of 20 fields with bop latent virus (HLV), and 9 of 13 fields containing American hop latent virus (AHLV) had incidences of <21%. Viruses were widespread in a research station which was the source of new material to commercial growers. No symptoms of virus infection were noted on New Zealand cultivars and viruses had no effect on growth of bines early in the season or vegetative growth at harvest of the cultivar ‘Superalpha’. The incidence of NRSV-I, ArMV-H, HMV, and HLV increased in only one of three fields in which evenly-spaced plants were tested for viruses over a 1- or 2-year period. The number of plants infected by NRSV-I and ArMV-H increased by 13 and 17% respectively over 1 year, whereas those with HMV and HLV increased by 21 and 8% respectively.