SummaryParticle preparations of parsnip yellow fleck virus (PYFV) isolates A‐421 and P‐121, representing the two major serotypes, were made by clarifying leal extracts with ether or butan‐1‐ol and concentrating the virus particles by precipitation with polyethylene glycol and differential centrifugation. The preparations containedc. 31 nm‐diameter particles comprising two sedimenting components. Top component (T) consisted of stain‐penetrable protein shells withA260/A280=0.8–0.9, sedimentation coefficient (S20) =56 S (A‐421) or 60 S (P‐121), and buoyant density = 1.297 g/cm3. Bottom component (B) consisted of nucleoprotein particles, not penetrable by negative stain, withA260/A280= 1.9, sedimentation coefficient (S020.w) = 148S(A‐421) or 153 S (P‐121), and buoyant density = 1.520 g/cm3(A‐421) or 1.490 g/cm3(P‐121). Yields of B component particles were up to c. 1 mg/100 g leaf tissue (both isolates); yields of T component particles were up toc. 0.6 mg (A‐421) or 5.5 mg (P‐121) per 100 g leaf tissue. PYFV particles were found to contain a single RNA species (mol. wtc. 3.4 × 106,c. 9800 nucleotides), constituting 40% of the particle weight, and three polypeptide species, of mol. wt (× 103)30, 26 and 24