P.carinii molecular epidemiology appears a new interesting investigational field to understand distribution and incidence of isolates from different geographical locations. Recently a typing system, the Type Specific Oligoblotting (TSO) based on 6 different sequences of the Internal Transcribed Spacers (ITSs) of P.carinii rRNA has been developed [1]. By using P.carinii ITSs nested PCR followed by TSO hybridization we have typed 55 lung derived specimens collected in Italy, The Netherlands and sub-Saharian Africa from pts with microscopically detected P.carinii pneumonia.