Technical Abstract: The intent of this document is to provide guidance on preparing for and conducting single-species tests to measure and evaluate the pathogenicity and/or toxicity of new microbial substances to aquatic and terrestrial organisms. This guidance and the associated testing is required by Environment Canada as part of the New Substances Notification Regulations in effect under the Canadian Environmental Protection Act, 1999. Examples of microbial substances and related products that might be covered under these guidelines are soil amendments for bioremediations, degradation products for fats and proteins that might clog up restaurant grease traps, compost enhancers, bio-filters, and septic tank activators. This document focuses on the information requirements, with respect to laboratory tests, for measuring the potential ecological effects of new microbial substances on the following organisms: aquatic plants, aquatic invertebrates, aquatic vertebrates, terrestrial plants, terrestrial invertebrates, and terrestrial vertebrates. The guidance is intended for notifiers, environmental consultants, study directors, and principal investigators. It will assist in the selection of a series of biological test methods for measuring the pathogenicity and/or toxicity of new microbial substances, as well as, in the planning, execution, and reporting phases associated with each test.