A Horn class is an axiomatizable class of algebraic systems, closed with respect to filtered products. The paper is concerned with a description of groupoids generating categorical Horn classes. The author gives a partial solution of this problem. The rank (h-rank) of a set \(X\subseteq A\) in an algebraic system \({\mathfrak A}\) is the length of a maximal chain of non-empty h-subset of X. This definition was introduced in the paper of E. A. Palyutin [Algebra Logika 19, 582-614 (1980; Zbl 0491.03011)]. It should be noted that the author of the reviewed paper uses the definition of this rank inexactly. The rank of any infinite set is, at least, 2 and so it is necessary to add 1 to values of ranks in all statements of the paper. It turns out that any system of rank 2 generates a categorical Horn class. Using the criterion of E. A. Palyutin for a Horn class to be categorical, a description of groupoids of rank 3 generating categorical Horn classes is found.