OBJECTIVES: To compare 2005 and 1995 ethics guidelines from journal editors to authors regarding requirements for institutional review board (IRB) approval and conflict-of-interest (COI) disclosure. DESIGN: A descriptive study of the ethics guidelines published in 103 English-language biomedical journals listed in the Abridged Index Medicus in 1995 and 2005. Each journal was reviewed by the principal author and one of four independent reviewers. RESULTS: During the period, the proportion of journals requiring IRB approval increased from 42% (95% CI 32.2% to (...) 51.2%, p<0.001) to 76% (95% CI 66.4% to 83.1%, p<0.001). In 2005, an additional 9% referred to the Declaration of Helsinki or the International Committee of Medical Journal Editors' Uniform requirements for ethical guidelines; 15% (95% CI 8.5% to 22.5%, p<0.01) provided ambiguous or no requirements. The proportion of journals requiring COI disclosure increased from 75% (95% CI 66.6% to 83.3%, p<0.05) to 94% (95% CI 89.4% to 98.6%, p<0.05); 41% had comprehensive requirements, while some addressed only funding source (6%), were vague (10%) or both (14%). Criteria for authorship rose from 40% (95% CI 30.5% to 49.5%, p<0.05) to 72% (95% CI 63.3% to 80.7%, p<0.05). Journals with higher impact factors were more likely to require IRB approval (p<0.01). Journals in anaesthesia and radiology all required IRB approval; requirements in other disciplines varied. CONCLUSIONS: Instructions to authors regarding ethical standards have improved. Some remain incomplete, especially regarding the scope of disclosure of COI. The ethical guidelines presented to authors need further clarification and standardisation. (shrink)