Objective: To analyse the time variation of topics in bioethical publications as a proxy of the relative importance.Methods: We searched the Medline database for bioethics publications using the words “ethics or bioethics”, and for 360 specific topics publications, associating Medical Subject Heading topic descriptors to those words. We calculated the ratio of bioethics publications to the total publications of Medline, and the ratio of each topic publications to the total bioethics publications, for five-year intervals, from 1970 to 2004. We calculated (...) the time variation of ratios, dividing the difference between the highest and lowest ratio of each topic by its highest ratio. Four topics were described, selected to illustrate different patterns of variation: “Induced Abortion”, “Conflict of Interest”, “Acquired Immunodeficiency Syndrome”, “Medical Education.”Results: The ratio of bioethics publications to total Medline publications increased from 0.003 to 0.012. The variation of the topic’s ratios was higher than 0.7 for 68% of the topics. The Induced Abortion ratios decreased from 0.12 to 0.02. Conflict of Interest ratios increased from zero to 0.07. The Acquired Immunodeficiency Syndrome ratios were nearly zero in the first three intervals, had a peak of 0.06 during 1985–9, followed by a decrease to 0.01. Medical Education ratios varied few, from 0.04 to 0.03.Conclusions: There was an increase of bioethical publications in the Medline database. The topics in bioethics literature have an important time variation. Some factors were suggested to explain this variation: current legal cases, resolution of the issue, saturation of a discussion and epidemiologic importance. (shrink)