.pgpass not working

Apologies in advance if this is the wrong place to ask.

I have Postres 8.4 and I am setting up replication with Slony. 

I'm having password issues with slony.

I have roamed the net for a solution and the way to fix it is to use the .pgpass file or change pg_hba.conf to accept trusted connections.

I do not want to touch the pg_hba.conf so I have generated the .pgpass file.

The permissions is set to 600, and I have correctly inputted the details into .pgpass, there are no leading spaces.

However I am still prompted for a password.

I have tested pg_dump as well and it prompts also.

Does anyone have any suggestions on what may be the culprit. Is there somewhere I need to specify to tell the system to look into the .pgpass file?

many thanks

rebecca