We present a statistical study of short-period fluctuations in the interplanetary plasma velocity and magnetic field, using spacecraft observations with a time resolution of 72 s (Pioneer 6) and 5 min (Mariner 5). The goal of our analysis is a characterization of the parent population from which all individual microscale events on these time scales are drawn. As a rough measure of the energy density of a given fluctuation we consider the quantity 1/2&rgr;‖V2-V1‖2+‖B2-B1‖2/8&pgr;, where &rgr;= (&rgr;1+&rgr;2)/2 and the subscripts denote any two consecutive observations. If we group microscale changes according to their energy densities as compared to the energy density of the background magnetic field, we find that each grouping exhibits the following statistical properties, within the limits of observational uncertainty. (1) The vectors (V2-V1) and B2¿B1 tend to be perpendicular. (2) The vector (V2-V1) has a strong tendency to be parallel or antiparallel to the vector (B2/&rgr;2-B1/&rgr;1). (3) The magnitude of ‖V2-V1‖ tends to be of the order of (&rgr;/4&pgr;)1/2 ‖B2/&rgr;2-B1/&rgr;1‖; however, there are a significant number of events with ‖V2-V1‖ much less than (&rgr;/4&pgr;)1/2 ‖B2/&rgr;2-B1/&rgr;1‖.