Clostridia were isolated from marine sediments collected in Puget Sound in the State of Washington. Sampling stations varied in depth from 10 to 240 m and sediment types varied from sand and gravel to reduced mud. Counts of bacteria growing both aerobically and anaerobically at 30 °C were made. Aerobic and anaerobic counts were 1.21 to 16.9 × 104and 0.73 to 23.5 × 104 cells/ml of sediment–water slurry respectively. About 30% of the bacteria growing anaerobically were obligate anaerobes and identified as Clostridia. The identified Clostridia fell into 12 groups. The first three groups, containingClostridium perfringens,C.bifermentans, andC.novyi, made up 76% of the isolates.The results show a variety of species of mesophilic Clostridia in marine sediments withC.perfringensisolated in the highest numbers.