The paper examines whether productivity differences among individual researchers are larger in some fields of learning than in others. Productivity patterns in the natural sciences, the medical sciences, the social sciences, and the humanities are compared by the use of unweighted and weighted publication counts. Irrespective of whether total number of publications or a refined indicator taking account of type of publication and multiple authorship are used, there are no essential differences in publishing inequality between the various fields. About 20% of the tenured faculty at Norwegian universities produce 50% of the total output, and the most prolific half of the researchers account for almost 85% of the output. The results are discussed in relation to Lotka's law.