Growth and normal pigment formation of Pseudomonas fluorescens and Flavobacterium deciduosum (isolated from cod fish slime) on nutrient agar have been observed at 0 °C, −3 °C. and −6.5 °C., the lowest temperatures recorded for any bacteria, except by Bedford in 1933—marine bacteria growing at −7.5 °C. Ps. fluorescens maintained motility at these temperatures for over five weeks, i.e. longer than at temperatures above 0 °C. Practically all cultural characteristics of these organisms and Achromobacter x were evident at −3 °C. Nitrate reduction, proteolysis of fish muscle protein and fluorescence on fish extract agar were the least cold-sensitive of the reactions, becoming evident at −3 °C. in as short periods as 5 days, 7 days and 12 days, respectively.Prolonged cultivation of the test-organisms at 5 °C. produced "adapted" strains, that were more active at 0 °C. and especially at −3 °C, than strains sub-cultured at 20 °C, 0 °C. or −3 °C. With few exceptions, no "adaptation" to cultivation at 0 °C. or −3 °C. occurred.With the exception of motility, none of the cultural characteristics of Pseudomonas fluorescens, Flav. deciduosum and Achromobacter were impaired by exposure to freezing at −16 °C. in distilled water and sterile sea-water for various lengths of time (8 minutes, 60 minutes, 44 hours) although from 40 to 70 per cent of the cells failed to grow on agar after 8 minutes' exposure and 99.9 per cent after 4¼ hours' freezing.