Hello,

I presume that no group should attend the same activity twice.

So:

Option Explicit

Public Sub gen5periods()

Dim i As Long
Dim j As Long
Dim k As Long
Dim brepeat As Boolean

Range("B2:B24").FormulaArray = "=uniqrandint(23,false)"
For i = 3 To 6
brepeat = True
Do While brepeat
Range(Cells(2, i), Cells(24, i)).FormulaArray =
"=uniqrandint(23,false)"
brepeat = False
For j = 2 To i - 1
For k = 2 To 24
If Cells(k, j).Value = Cells(k, i).Value Then
brepeat = True
End If
Next k
Next j
Loop
Next i

End Sub

My function UniqRandInt() you can find at:
http://www.sulprobil.com/html/uniqrandint.html

HTH,
Bernd