[en] We present a detailed study of the physical conditions and chemical composition of the interstellar medium in line to HD 93205, an 03V star embedded in the Great Carina Nebula. We have identified up to six components in the ultraviolet absorption lines, spanning a velocity range of 375 km s^-1. The two main high-velocity components have been found to show different relative abundance patterns. The red-shifted component shows no depletion. For the blue-shifted component, the relative abundance pattern seems difficult to explain in terms of elements locked into grains; we tentatively attribute its composition to mixing with freshly synthetized material ejected by a recent supernova explosion. Among the two low-velocity components, one has been identified with the normal interstellar gas in the disk of the Galaxy. In this component we have measured column densities of interstellar CIV and SiIV, free from contamination by circumstellar material. The other low-velocity component has been identified with the approaching part of the expanding ionized nebula around the Carina OB associations. It consists of a dense HII region in which the two conspicuous OI fine-structure lines originate