In a serologic and cultural survey of 127 brush-tailed possums (Trichosurus vulpecula) occupying pasture land in New Zealand, leptospires of the Hebdomadis serogroup were obtained from 48 (38%) of the animals sampled. Eight isolates were identified by cross-absorption agglutin ation studies as being Leptospira interrogans serovar balcanica. There was a marked age difference in prevalence with 41 positive cultures from 64 mature adults (64%) and no recoveries being made from juveniles. Isolation of leptospires was aided by the use of a new technique involving the homogenation of whole kidneys in gamma sterilized plastic bags in a "Coleworth Stomacher". The use of this apparatus allowed the processing of whole kidneys and the technique was efficient in both the recovery of leptospires and the prevention of contamination. In view of the fact that serovar balcanica has been recorded previously only in East Europe in man, cattle and pigs, the high prevalence of infection in a wild animal population in New Zealand is an interesting development in the world distribution of this serovar.