SUMMARYIn New Zealand, all garlic (Allium sativum) plants tested were infected by a virus with flexuous filamentous particles 700–800 nm long. This virus, called garlic yellow streak virus (GYSV), infected only two of 12 species tested and was transmitted to garlic by the aphidMyzus persicaein a non‐persistent manner. In garlic sap, GYSV was infective at a dilution of 10‐4but not 10‐3, after heating for 10 min at 60°C but not 65°C, and after 2 days but not 3 days at 25°C.The yield of virus, purified from naturally infected garlic, was 3–4 mg/kg fresh leaf. Preparations hadA260/A280= 1.28 andAman/Amin= 1.08. The virus particles had a sedimentation coefficient of 149S and a buoyant density in CsCl of 1.334 g/cm3. Mol. wt estimates for the virus nucleic acid were 2.95 × 106by electrophoresis in polyacrylamide gels and 3.46 × 106from the sedimentation coefficient (41.4S) in linear‐log sucrose density gradients. Two polypeptides were detected in virus preparations; one (mol. wt 30 500) was possibly a breakdown product of the other (mol. wt 33 000). GYSV was serologically distantly related to onion yellow dwarf and leek yellow stripe viruses but was considered to be a separate virus because it differed from th