Enhancements of strange baryon and anti-baryon yields were first observed in Pb-Pb interactions at 160 A GeV / c by WA97. The aim of the NA57 experiment is to investigate how these enhancements behave as a function of energy, and over a broader centrality range than that which was available with WA97. This paper presents a comparison of the hyperon yields in Pb-Pb interactions at 40 A GeV / c and 160 A GeV / c. Preliminary signals for the p-Be data at 40 A GeV / c are also shown.