The DNA sequence of the gene coding for the OXA-2 beta-lactamase has been completed. The primary amino acid sequence deduced from the DNA sequence was used to study homologies with other beta-lactamases; no good homologies were observed with any class of beta-lactamase. A more detailed analysis has revealed from comparison of both primary and predicted secondary structure, that the OXA-2 beta-lactamase may be more closely related to class A enzymes. Confirmation that the OXA-2 beta-lactamase is a serine enzyme has come from the DNA sequence and the interaction with mechanism based inactivators. Clavulanic acid and a novel beta-lactamase inhibitor, BRL36148, both interact specifically with the OXA-2 beta-lactamase by branched pathway mechanisms. Analysis of inactivated enzymes by peptide mapping and isoelcetric focusing have revealed that more than one inactive enzyme species is formed with each inactivator. A specific DNA probe was designed to come entirely from within the coding sequence of the OXA-2 beta-lactamase gene. This probe was found to interact only with plasmids specifying the OXA-2 or OXA-3 type enzymes. These results confirm earlier observations that OXA-2 and OXA-3 beta-lactamases are related. Another probe which comprised the whole of the OXA-2 beta-lactamase gene as well as segments of DNA on either side of the gene, was found to hybridise with a number of resistance plasmids. This interaction suggests that multi resistance plasmids carry common segments of DNA. Characterisation of the physical properties of the OXA-2 enzyme by analytical ultracentrifugation have not only confirmed the dimeric nature of this beta-lactamase but have also shown that this enzyme forms aggregates at high protein concentrations. Probing of the enzyme structure with trypsin, strongly points to the OXA-2 beta-lactamase having a domain structure.