Well Dieter, that worked like a charm. Thanks a lot. I already had the REQUEST object in the External method (although I'll have to admit that I don't have a clue as how to it is actually passed.) I just added from DateTime import DateTime REQUEST.RESPONSE.setHeader('Expires',DateTime(DateTime().timeTime() + 3600).toZone('GMT').rfc822()) REQUEST.RESPONSE.setHeader('Last-Modified', self.bobobase_modification_time().toZone('GMT').rfc822()) in the right places and everything seems to work fine. One other thing. Zope aknowledges changes to Data.fs on the fly but to get it to react to changes in External methods I have to restart zope. During debugging this is kind of tiresome. There must be a simpler way. Right? -- oivvio polite cell +46 (0)709 30 40 30 / phone +46 (0)8 669 64 18 / fax +46 (0)8 84 00 18 varvsgatan 10A / s-117 29 stockholm / sweden