Efforts have been made to endorse the thory of a viral aetiology for the feline urolithiasis syndrome (FUS) in the male cat. The presence of virus in the urine of three cases could not be confirned nor could the condition be transmitted by intra vesicular inoculation of urine from four affected cats into the bladders of normal cats. Following these negative findings work was done on SPF cats and a survey made of the incidence of urethral obstruction in six SPF cat units in England. No cases were reported from four of these units over a two-year period. Five cases occurred in the other two SPF units, three of which were associated with feeding an expanded dry cat food. There is, thus, no direct evidence that viral agents are involved in the aetiology of FUS.