Does the machine have a lot of ram (2+ GB)? If so, you may want to enable
the /3gb switch.

Check with perfmon where the memory goes ;-), the "CLR memory" gen0 .. 2 and
Harge Object Heap counters shows you the managed heap consumption, while
"process" - private bytes tells you about both managed and native heap
consumption (the managed heap itself is a native heap).

If it happens that your gen2 counter grows and doesn't shrink when a full
collection occurs, you have to inspect your code as you are keeping object
references alive (places to look at are arrays, arraylist and collections).
If the LOH grows (containing objects > 85 Kb) it means that - or you are
holding LOH references, or the LOH is getting fragmented, in the latter case
there is only one thing you can do - shutdown the service (or application
domain) and restart.

If your gen 0 ..2 counters show a normal allocation pattern (that is
growing/shrinking), but private bytes keep growing, you have a unmanaged
leak (note that you always call unmanaged code, be indirectly or directly).

Willy.