Updated project metadata. When studying gene expression in microbe-animals symbioses collected in the field it is essential to quickly and efficiently preserve in situ symbiont and host gene expression patterns. One of the most commonly used sample preservation methods for samples targeted for proteomic analyses is flash freezing, however, liquid nitrogen or dry ice needed for flash freezing are often not available at remote field sites. We tested if RNAlater allows to preserve proteins in animal-microbe symbioses as efficiently as flash freezing and without introducing issues with downstream processing. We used the marine gutless oligochaete Olavius algarvensis as a model for testing. Olavius algarvensis lives in shallow water sediments off the coast of Elba, Italy. It has no digestive and excretory system and harbors five bacterial symbionts that fulfill its nutritional and waste recycling needs (Kleiner et al., 2012, PNAS 109(19):1173-82). We compared five RNAlater preserved and five flash frozen samples in terms of the number of identified proteins, abundances of individual proteins and potential biases against specific protein or taxonomic groups. Five worms were incubated in RNAlater for 24 hours. After incubation, RNAlater was removed and samples were stored at -80°C. The remaining five worms were preserved with liquid nitrogen and stored at -80 °C immediately after preservation.