Uranium contents and 234U/238U radios were determined in 2 samples of Mediterranean and Atlantic seawater by α-spectrometry. The Mediterranean waters present salinities often higher than 38‰. This allowed us to test the relationship between their uranium content and salinity (U-S), already defined for a salinity interval from 30.3 to 36.2‰. The uranium content of the Mediterranean waters is higher than predicted by the U-S relationship which might be due to the fact that 1) the relationship established for lower salinities cannot be extrapolated to high salinities or 2) Mediterranean waters present higher uranium content, possibly due to phosphate fertilizer inputs. There is an abridged English version. -English summary