Just to add to everyone elses suggestions.  Take a look at the MAX472.  
Should be able to design it for whatever range you want.

Jinx wrote:

>Any circuit suggestions for a multimeter plug-in that could measure
>1nA (hopeful) to a few uA ? I was thinking perhaps A -> V and
>use the low DC volts range
>
>I've got a couple of multimeters - one goes down to 20uA and the
>other to 2000uA. Measuring a sleeping 12F675 gets you 00.0uA
>or 0.000mA (yes, it is alive, I can wake it up to do stuff). Helpful
>in the sense that it shows the battery will last a flipping long time,
>but there's nothing there to hang your hat on
>
>Googled and Googling around a bit but not too fruitful yet. Maybe
>I'm not searching for the right thing, and there's such a bewildering
>array of parts and technologies I might not even recognise what I
>need when I see it anyway
>
>The old NatSemi Linear Apps book has a 200pA-100uA circuit
>(LB37) for the LM216A and a 100uA  moving coil meter, but the
>LM216A seems to have dropped off the radar. I'm certain there
>will be an equivalent or better around, but short of downloading
>squillions of op amp datasheets...........
>
>TIA
>
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