>How do I stop the timer firing while in a timer event?
>Lets say I have a timer, tim1, on a form.
>If the first line of the tim1.timer() event is
>this.enabled= .F.
>shouldn't that stop the timer firing again.

Yes. According to the docs for the VFP7 .Enabled property:

Disabling a Timer control by setting Enabled to false (.F.) cancels the countdown specified by the Timer control's Interval property.

>Yet if I debug and step through the code, the timer keeps firing.
>If I put
>this.interval= 0
>in the first line the debugger stops and looses its place.
>I'm sure I used to be able to do this somehow??

Have you tried a really basic test, like maybe using a WAIT WINDOW, not in the debugger? Is there anything else unusual in the environment like an ActiveX?

>Also, if my timer() code takes 2 seconds to run and the interval is set to 500 milliseconds, the timer seems to re-fire whilst in the middle of the code execution. Should that be?

Certainly. That's why you need to disable it while its event is running.