IMPLEMENTATION OF MOLECULAR SWITCHES. In order to plan for integrated circuits of ever greater complexity and compactness, computer engineers would like "grow" components and interconnections with chemical self-assembly instead of building them with lithography. The next step toward creating such nano-scale computer circuits, once the discrete molecular units have been assembled, is to wire them up and configure them into logic gates (OR, AND, etc.). This has now been done by a Hewlett Packard/UCLA/Berkeley team, which has set itself the task of producing a working 16-bit memory cell, no larger than a square 100 nm on a side, within two years. In the 16 July issue of Science, the team reports on an experiment in which an array of rotaxane molecules, grown on a substrate, are controlled by a grid of wires which, through a system of applied voltages trigger local chemical reactions at each rotaxane. These reactions serve to configure the rotaxanes which become in effect molecular-scale switches whose resistivity in the "on" state is 80-100 times less than in the "off" position. Furthermore, addressing the rotaxanes and reading out their condition will require only two wires per molecule rather than the four wires typically needed in conventional integrated circuits based on the complementary metal oxide semiconductor (CMOS) design.