Several properties of B.subtilis phage SP02 are described and compared with two other phages, SPP1 and φ105. All three phages are similar in morphology and size; each has a hexagonal-shaped head, which is probably a regular icosahedron, and a long flexible tail without a sheath. SP02 and φ105 have complex structures at the base of the tail which consist of six subunits surrounding a central core. The diameter of the head of SP02 is 495 Å and the length of the tail is 1770 Å. Phages SP02 and φ105 are antigenically related. The DNA from SP02 and SPP1 phage particles is very similar in molecular weight (25-26 × 106 daltons). The DNA from phages SP02, SPP1 and φ105 is infectious in a transfection system. The DNA from SP02 phage has cohesive ends. © 1969.