An IBM-compatible microcomputer was used to enable an LKB Ultrospec II UV-Visible spectrophotometer to perform two features which are not available on the basic unit: wavelength scanning and enzyme kinetic analyses. The spectrophotometer was controlled using a simple BASIC program, an RS232c interface and the instrument's own built-in microprocessor. This technique required no special analogue to digital conversion hardware or software and only a rudimentary knowledge of programming. User-designed software permits a greater degree of flexibility in routines and output formats than is offered in most pre-programmed instruments, while offering substantial savings.