Sorry, it seems I didn't click on the right button :), here is the message sent to the list this time : Thank you Andreas for showing me this nice tool which is tcpflow. Thanks to it, I am now sure that the probleme is coming from zope. Would you take a look at this : root@CAY:~/HTTPCONNECTIONS# tcpflow host 10.75.49.100 and port 8081 tcpflow[20104]: listening on eth0 The tcpflow is run on the 10.75.49.51 machine, the one that zope thinks it sends two times the XMLRPC query. 10.75.49.100 is the server that runs zope. Now i click on the button, on both browsers (remember they are on different machines), invoking the method "toutCompter" via xmlhttprequest, and wait for zope to complete the requests : <zope trace to the console> ip: 10.75.49.155 requests counting of lines 1 to 11 ip: 10.75.49.51 requests counting of lines 1 to 11 sending results to 10.75.49.155 sending results to 10.75.49.51 ip: 10.75.49.51 requests counting of lines 1 to 11 sending results to 10.75.49.51 </zope trace> Zope says he got 2 requests form 10.75.49.51 and sent it the results 2 times. Ok, let's check the tcpflow then for these supposed connections : root@CAY:~/HTTPCONNECTIONS# ls total 8,0K -rw-r--r-- 1 root root 873 2007-01-18 18:52 010.075.049.051.41131-010.075 .049.100.08081 -rw-r--r-- 1 root root 607 2007-01-18 18:53 010.075.049.100.08081-010.075.049.051.41131 Allright, first file (machine to server): root@CAY:~/HTTPCONNECTIONS# cat 010.075.049.051.41131-010.075.049.100.08081 POST /aef/rechercheMultiligne/toutCompter HTTP/1.1 Host: 10.75.49.100:8081 User-Agent: Mozilla/5.0 (X11; U; Linux i686; fr; rv:1.8.1) Gecko/20061010 Firefox/2.0 Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9 ,text/plain;q=0.8,image/png,*/*;q=0.5 Accept-Language: fr,en-us;q=0.7,en;q=0.3 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-15,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Content-Type: application/x-www-form-urlencoded Referer: http://10.75.49.100:8081/aef/rechercheMultiligne Content-Length: 224 Cookie: _ZopeId="58653529A2r8NuahgXc" Pragma: no-cache Cache-Control: no-cache requete_1=ape%2012*&requete_2=ape%2012*&requete_3=ape%2012*&requete_4=ape%2012*&requete_5=ape%2012*&requete_6=ape%2012*&requete_7=ape%2012*&requete_8=ape%2012*&requete_9=ape%2012*&requete_10=ape%2012*&borneInf=0&borneSup= 10&root@CAY:~/HTTPCONNECTIONS# Allright, there is only ONE POST request. So zope didnt really got two requests. Now let's see if it sent the data two times as it presumes : root@CAY:~/HTTPCONNECTIONS# cat 010.075.049.100.08081-010.075.049.051.41131 HTTP/1.1 200 OK Server: Zope/(Zope 2.9.0-, python 2.4.2, linux2) ZServer/1.1 Date: Thu, 18 Jan 2007 17:51:42 GMT Content-Length: 413 Charset: utf-8 Content-Type: text/xml; charset=utf-8 <?xml version="1.0" encoding="utf-8" ?><comptages><comptage numLigne="1">3</comptage><comptage numLigne="2">3</comptage><comptage numLigne="3">3</comptage><comptage numLigne="4">3</comptage><comptage numLigne="5">3</comptage><comptage numLigne="6">3</comptage><comptage numLigne="7">3</comptage><comptage numLigne="8">3</comptage><comptage numLigne="9">3</comptage><comptage numLigne="10">3</comptage></comptages> root@CAY:~/HTTPCONNECTIONS# The results were sent just one time, not two. What is going on here ? Any comment would be really appreciated. Thanks, Y.Chaouche