Annual variations of vibrios able to proliferate at 37 degrees C have been studied in various conditions: in urban waste water discharged in the Toulon harbour, in mussels subjected or not to those discharges, and in seawater far from the waste water effluent (for reference). Mean concentration values were nearly similar in the effluent and seawater samples, in the order of 500 bacteria/100 mL, and 400 bacteria/mL in ground mussels, with concentrations showing great variability. In all cases, seasonal abundance fluctuations occurred, with a minimum in winter. A total of 214 vibrio strains were analyzed and identified. The effluent population was the most diversified, including several species of sanitary interest such as Vibrio fluvialis (29.3%), V. cholerae (non O1) (13.4%), and V. metschnikovii (11.0%), as well as other species more typically marine, notably V. alginolyticus (11.0%). In seawater, the latter species was largely represented (48.6%), but other representatives of this genus were also present, such as V. harveyi, V. campbellii, or V. fishcheri; no strain of V. metschnikovii was isolated. The specific composition of the population associated with mussels was similar to that found in seawater.