Well, the time can be reduced. This averages about 270ms on my box: #include <Array.au3> Global $MyArray1[1200] For $n = 0 To UBound($MyArray1) - 1 $MyArray1[$n] = $n Next Global $MyArray2[500] For $n = 0 To UBound($MyArray2) - 1 $MyArray2[$n] = ($n * 2) + 1; Odd numbers only Next Global $iTimer = TimerInit() $avResult = _ArrayDiff($MyArray1, $MyArray2) $iTimer = Round(TimerDiff($iTimer), 2) & "ms" _ArrayDisplay($avResult, "Time = " & $iTimer) ; ----------------------------