I recently reported in this journal some observations on the structure of Sericesthis iridescent virus (SIV) (Wrigley, 1969). In this short communication I report similar observations on the closely related Tipula iridescent virus (TIV) and interpret them in the same way. The TIV used in this study was obtained from Dr S. Tojo, Tokyo University. It was treated in aqueous suspension in the same way as SIV by mixing at room temperature with an equal volume of the nasal decongestant ‘Afrin’ (‘Drixine’, Schering Corp., New Jersey, U.S.A.). The result of this treatment was the same as for SIV; protein subunits (i.e. morphological units or capsomeres) on the particle surface were revealed by negative stain (4% (w/v) potassium phosphotungstate, pH 7) in the electron microscope. About 10% of the particles reacted in this way, but after only 24 hr, compared to 48 hr for SIV.