Why won't this string operation work?

[MrNorth]

string tS = "JOB !12 JAN 2002 ! 12:22:12";

tS.Replace("2","r");
Console.Write(tS);

the output is:
JOB !12 JAN 2002 ! 12:22:12

although the replace method should have replaced the 2 with r


HOWEVER

this one works
Console.Write(tS.Replace("2","r"));

Anyone has any suggestions???

best regards
Henrik