[SouthwaterDave]

Here's one way, using regular expressions...

Imports System.Text.RegularExpressions
 
Module Module1
      Sub Main()
             Dim source As String = "Hello", target As String = ""
 
             For Each m As Match In Regex.Matches(source, "[aeiou]")
                    target &= m.Value
             Next
 
             Console.WriteLine(target)
      End Sub
End Module