The purpose of this article is to provide information about author productivity as reflected through the number of occurrences of personal name headings in the Slovenian online catalogue COBIB. Only authors associated with monographs are treated. So, author productivity of monographs that has not been widely researched is empirically examined to determine conformity or nonconformity to Lotka’s law. A random sample of 1.600 Slovenian authors is drawn from the authority file CONOR. Next, the authors are searched in COBIB and each attributed the number of monographs. Using the formula: xny = c, the values of the exponent n and the constant c are computed and the Kolmogorov-Smirnov test is applied. The paper shows that the author productivity distribution predicted by Lotka also holds for the occurrences of personal name headings in COBIB.