Thanks, Greg.

I was wondering if I am on the right lines with something like this (taken a few options out until I achieve something that works)? I like the idea of highlighting the missing TextBox / ComboBox with a border colour.

Private Sub EnterBut_Click()

    If cbThreat.ListIndex < 1 Then
        MsgBox "Select threat level!", vbExclamation + vbOKOnly, "Triage Hub"
        cbThreat.SetFocus
        cbThreat.BorderColor = RGB(255, 0, 0)
        GoTo lbl_Exit
        
    ElseIf cbThreat.ListIndex < 1 Then
        cbThreat.BorderColor = RGB(0, 0, 0)
        GoTo lbl_Exit
    End If
    
    If Trim(txtResearch.Text & "") = " " Then
        MsgBox "Enter Research", vbExclamation + vbOKOnly, "Triage Hub"
        txtResearch.SetFocus
        txtResearch.BackColor = RGB(255, 0, 0)
        GoTo lbl_Exit
    ElseIf Trim(txtResearch.Text & "") <> " " Then
        txtResearch.BackColor = RGB(0, 0, 0)
        GoTo lbl_Exit
    End If

    Tag = 1
    Hide
lbl_Exit:
    Exit Sub
End Sub