The β‐lactamase‐inhibiting activity of 6m‐ethyl‐pyrid‐2‐yl‐ammine palladium‐dichloride (Pd 25 681) and cis‐dichloro‐diammine‐platinum (II) was studied and compared with the enzyme inhibitory action of potassium clavulanate and the penicillanic acid sulfone CP 45899. Using the nitrocefin test method and the TITERTEK/Microtiter equipment CP 45 899 and potassium clavulanate were the strongest inhibitors of the Bacillus cereus β‐lactamase. Cis‐dichloro‐diammine‐platinum(II) was fourfold less active than the palladium complex Pd 25 681 in äquimolar concentration. The following ID50 values were found: CP 45 899: 0.0281 μg; K‐clavulanate: 0.1274 μg; Pd 25 681: 3.8603 μg; cis‐dichlorodiammine‐platinum(II): 12.5120 μg/100 μl.