The detection of antimicrobial residues in ex-farm, bulk, raw, cows' milk by the Delvo X-Press β-lactam test and by the Delvotest P was compared. Of 500 samples, 499 gave the same results by the two procedures. One sample classified as Delvotest P-negative gave a borderline positive result with the Delvo X-Press test but a negative result upon re-test. Fifty samples giving positive results by the ... [Show full abstract] Delvotest P procedure were also positive by the Delvo X-Press test; all contained penicillinase-sensitive β-lactams. The results of this study indicate that the Delvo X-Press test could accurately detect β-lactams in bulked, ex-farm raw milks.