Pass variable from 1 section of code to another

Hi
Can anyone tell me how I can get the value of strOrderNumber to display in lblDisplayOrderNumber.Text
lblDisplayOrderNumber is in a different panel to strOrderNumber.

Regards
Caz

private void btnProceed_Click(object sender, System.EventArgs e)
{
// code
strOrderNumber = "Order number" + " " + sqlComRetrieveOrderNumber.Parameters["@RETURN_VALUE"].Value.ToString();
}

private void btnCheckDetails_Click(object sender, System.EventArgs e)
{
lblDisplayOrderNumber.Text = strOrderNumber;
}