Newbie: Webservice String Function question

Why do i get this message when i try to run it as a webservice?
First "Name 'TRIM' is not declared." Then "Name 'REPLACE' is not declared."

This is the code i use:
<%@dotnet.itags.org. WebService language="VB" class="test" %
Imports System
Imports System.Web.Services
Imports System.Xml.Serialization

Public Class test

<WebMethod> Public Function Add(a As Integer, b As Integer) As Integer
Return a + b
End Function

<WebMethod> Public Function WebTrim(a As String) As string
Return TRIM(a)
End Function

<WebMethod> Public Function WebReplace(a As String) As string
Return REPLACE(a, "e", "f")
End Function

End Class

If i run is like a normal web page it works perfect.
I'm using Webmatrix and have reinstalled all met .net components.

Please help me.

Thanx in advancehave you tried the OO way?

return a.Trim()

return a.Replace("e","f")
Thanx for the quick repley but i found wath it is.
This one i missed:
Imports Microsoft.VisualBasic