what is myArray1? do all 3 arrays have the same number of elements? to be safe, i would loop thru each of the 2 arrays individually, which you're doing anyway....
dim max_val
max_val = 0
For i = 0 to UBound(myArray2)
If (max_val < myArray2(i)) Then
max_val = myArray2(i)
End If
Next...