In S. G. Matthews [Partial metric topology, in: Proc. 8th Summer Conference on General Topology and Applications, in: Ann. New York Acad. Sci., vol. 728, 1994, pp. 183-197], the author introduced and studied the concept of partial metric space, and obtained a Banach type fixed point theorem on complete partial metric spaces. The present paper forms part of the study of possible extensions of metric fixed point results to the context of partial metric spaces, in particular two theorems due to Fisher. The theory is illustrated by some examples.