Many sequence analysis problems involve consideration of a multiple sequence alignment where the 3-dimensional structure of one (or more) of the aligned sequences is known. In such cases, it is useful to map the sequence variability onto the atomic co-ordinates of known structure. If the structure also includes a bound ligand (or the location of the active site is known), each column position in the multiple sequence alignment may be annotated with its 'distance' from the binding site. These annotations, together with a measure of sequence variability, provide additional insights into drug specificity, for example among viral mutants. This paper describes several useful programs that automate this analysis.