Olive pulp (OP) and its effluents produced after digestion processes were characterised and their suitability as soil amendment materials were investigated. Results showed that OP and its effluent for hydrogen (EH2) and methane production (ECH4) contain high amount of organic matter, remarkable concentration of nutrients and negligible content of heavy metals. Decreasing concentrations of low molecular weight phenols (monomeric phenols) and increasing amount of humic-like materials were found passing from OP to EH2 and ECH4. The effects on both wheat seed germination and seedlings growth were also investigated. Addition of OP at the highest doses delayed both seed germination and seedling growth. These effects decreased when the OP and its effluents were incorporated into the soil. On the contrary an enhancement of seedlings growth was detected by addition of EH2 and ECH4. Enhancement effects also were found out by addition of lower OP concentrations. The phytotoxic effects decreased when the products were incorporated into the soil. (c) 2006 Elsevier B.V. All rights reserved.