Sampling of soil causes changes in its natural environment: among others, soil structure and aeration status are disrupted and soil temperature and moisture are usually affected. This results in changes of soil microbial biomass and disruption of important biological processes. Although in general not recommended (Anderson, 1987), soil samples are often stored after sampling and before analyses, as for various reasons they cannot be processed immediately. The objective of this study was to assess the impact of soil storage on microbial biomass and its activities. Soils were sampled in several sites in the Czech Republic, mostly from plots of long-term field experiments (soils Jaro, Lipa, Luka, Iva) or from ordinary fields (soils from Netrebice and Chelcice). Microbial biomass, bazal and glucose-induced respirations and nitrifying activity were determined using standard methods; the results are expressed per gram of dry soil. As shown in Fig. 1, storage of most soils at 4 +/- 2 degrees C influenced microbial biomass. After one week storage, both increase and decrease of microbial biomass were recorded. During further storage (after 18 as well as 60 weeks) decrease of microbial biomass was found. However, only small fluctuations of microbial biomass but large increases of bazal respiration were found in soil stored at constant moisture at laboratory conditions (18 to 25 degrees C) for 56 weeks (Tab. I). Microbial biomass in air-dried soil first increased, but then decreased, while bazal respiration was slightly increased (Tab. II). Glucose-induced respiration fluctuated at the beginning of soil storage at 4 +/- 2 degrees C and decreased later on (Fig. 2). Nitrifying enzyme activity was determined in refrigerated (4 +/- 2 degrees C) as well, as in frozen (-20 degrees C) soils, the latter defrosted quickly (2 hours) and/or slowly (2 days) before the measurements. As shown in Fig. 3, it was enhanced in soils after 2 and 11 weeks of storage at 4 +/- 2 degrees C. When the frozen soils were defrosted quickly, the activity was significantly lower, while in soils defrosted slowly it was significantly higher in comparison with soils stored at 4 +/- 2 degrees C. The results showed that microbial biomass and its activities can be substantially changed during the storage of soils after sampling. It was also found that various soils (that is soils from different sites or differently fertilized soils) can respond differently. It is likely that after sampling there is a few days’ fluctuation period of control and regulatory factors, which is then reflected in fluctuation of microbial biomass and activities. Although Stenberg et al. (1998) recommend freezing when soils are to be stored, our results show that microbial activities in defrosted soils can be substantially changed. When processing freezed soils, the critical step is defreezing. We suggest that refrigeration of soils at about 4 degrees C is the most careful mode of storage but not even in this case uncontrolled changes in soils can be excluded.