SummaryBacteria made up an average of 90 per cent of the microbial populations of twenty‐four soil samples, mainly of the A0H horizon, from four peat‐podzol transitions.Bacillusspp., which averaged 67 per cent of these bacteria, were usually the predominant group. Gram‐negative non‐spore‐forming organisms (15 per cent),Streptomyces(8 per cent), and Gram‐positive cocci (5 per cent) occurred irregularly andArthrobacterandNocardiastrains rarely. A large proportion of the strains utilized glucose and malate, and a smaller proportion starch, citrate, and protein. A few strains liquefied pectin but none decomposed cellulose or xylan. In eight populations examined, 80 per cent of the bacteria required yeast extract for growth. Fungi usually formed only a small proportion of the populations. All the species, exceptPenicillium nigricansandTrichoderma viride, were isolated from only one transition. Yeasts occurred irregularly, usually in small numbers. Whilst no microbial group responded to the addition of glucose, nitrate, and phosphate to two soil samples, bacterial numbers increased after the addition of peptone and ye