A comparative study was performed on compost extracts prepared from cattle rumen content composted for three and nine months, nine month old compost inoculated with a Nutri-Life 4/20(TM) inoculum, and two commercial preparations (LivingSoil(TM) and Nutri-Life 4/20(TM)), all incubated for 48 h. Nutri-Life 4/20(TM) had the highest concentrations of NO(3)(-)-N and K(+)-K, while rumen compost extract had higher humic and fulvic acids concentration. The bacterial and fungal community level functional diversity of three month old compost extract and of LivingSoil(TM), assessed with Biolog(TM), were higher than that of nine month old rumen compost extract, with or without Nutri-Life 4/20(TM) inoculum, or Nutri-Life 4/20(TM). No difference in fungal diversity was observed between treatments, as indicated by Denaturing Gradient Gel Electrophoresis (DGGE) analysis, however, bacterial diversity was higher in all compost extracts and LivingSoil(TM) compared to the Nutri-Life 4/20(TM). Criteria for judging the quality of a microbially enhanced extract are discussed. (C) 2011 Elsevier Ltd. All rights reserved.