Problem: Value of a variable is lost on second postback

Hi everyone,

I found that the value of a variable(string type for example) is lost after the aspx page postback.

E.G:
private void Page_Load(object sender, System.EventArgs e)
{
if(!IsPostBack)
abc = "xyz";
}
private void Command1_Click(object sender,System.EventArgs e)
{
Response.Write(abc);
}

I have assigned the abc value to "xyz" , but after i click the command button, i found that the value of abc is lost. The code " Response.Write(abc)" shows nothing .May i know what's wrong with it ? Thx a lot