Blue-green algae virus LPP-1 has a head capsid hexagonal in projection, with edge-to-edge distance of 600 ± 20 A, and a short tail 200 A long and 150 A in diameter attached to one of the head capsid vertices. These observations made on intact virus particles have been extended by electron microscopic and preliminary chemical characterization of separated heads and tails. Purified heads dissociated in 6 M urea show a single band on acrylamide gel electrophoresis at pH 9; this component of the head protein elutes from a calibrated G-100 Sephadex column in a volume corresponding to a molecular weight of 17,500. Since the molecular weight of the total head protein is 24–28 × 10 6, the head is comprised of 1400–1600 structure units. Purified tail preparations contain at least three distinguishable particles: cylinders 200 A long × 105 A in diameter, capped cylinders 300 A long, and joined cylinders 400–450 A long. These probably correspond to tails without capitals, tails with capitals, and tail dimers, respectively. End views of the tail include pinwheels on which six elements are clearly resolved.