This invention provides methods and compositions for producing 
high titer, substantially purified preparations of recombinant adeno-associated 
virus (AAV) that can be used as vectors for 
gene delivery. At the onset of vector production, AAV producer cells of this invention typically comprise one or more AAV packaging genes, an AAV vector comprising a 
heterologous (i.e. non-AAV) 
transgene of interest, and a 
helper virus such as an adenovirus. The AAV vector preparations produced are generally replication incompetent but are capable of mediating delivery of a 
transgene of interest (such as a therapeutic 
gene) to any of a wide variety of tissues and cells. The AAV vector preparations produced according to this invention are also substantially free of 
helper virus as well as helper viral and 
cellular proteins and other contaminants. The invention described herein provides methods of producing rAAV particles by culturing producer cells under conditions, such as temperature and pH, that promote release of 
virus. Also provided is a quantitative, high-
throughput assay useful in the assessment of viral 
infectivity and replication, as well as in the screening of agent that affect viral 
infectivity and / or replication.