Based on http://vadmyst.blogspot.com/2008/02/when-stringtolower-is-evil.html

void DoBadAction (string val)
{
if (val.ToLower() == "somevalue")
{ //do something
}
}

Best method to do such kind of case insensitive comparison is using string.Equals(...) method.

void DoGoodAction(string val)
{
if (val.Equals("somevalue", StringComparison.OrdinalIgnoreCase))
{ //do something
}
}