An isolate of apple mosaic virus, designated ApMV‐J, was isolated from rose cv. Sweet Surrender in New York State, USA. Mechanical transmission of ApMV‐J from rose to cucumber was facilitated by preparing inocula with 0.03 M sodium phosphate buffer containing 0.02 M 2‐mercap‐toethanol and 1 % polyvinylpyrolidone. Catharanthus roseus cv. Little Linda was a good virus maintenance host and Cucumis sativus cv. Lemon a good propagation host. Contaminating host proteins were substantially reduced by including polyethylene glycol in the purification protocol. Purified virus had high A260/280 nm values and contained virus particles of c 25—26 nm in diameter; most particles were isometric but a few were bacilliform. The M.Wts. of the four nucleic acids of ApMV‐J, determined in non‐denaturing and denaturing agarose gels, were estimated at 1.16, 0.98, 0.68 and 0.35 × 106 and 1.0, 0.91, 0.66 and 0.35 × 106, respectively. The viral coat protein M. Wt. was estimated to be 27 kDa.