This work represents the first attempt to evaluate the precision of the specific oxygen uptake rate method expressed in terms of repeatability (r) and reproducibility limits (R). Three laboratories were involved in an inter-laboratory test for the validation of respiration analyses on six biomass samples (three composts and three biostabilized products) having different degrees of biological stability. Both the maximum specific oxygen uptake rate peak (SOUR) and the cumulative oxygen demand after 12 h (OD12) and 20 h (OD20) of respiration test were investigated. Precisions expressed as the relative standard deviation were in the range of 9-41%. Linear regressions found for r and R, versus OD12 and OD20, enabled derivation of precision values (r and R) for all respirometric levels within the operating range. The OD12 and OD20 indices were found to be more adequate to indicate biological stability since they were less influenced by random errors than the SOUR index. (c) 2006 Elsevier Ltd. All rights reserved.