Few general-purpose computer programs are available that analyze sequential categorical data. If there were a sequential data interchange standard—a standard way of representing sequential data—then it would be more attractive to write general-purpose computer programs for such data Moreover, interlaboratory sharing would be facilitated. The present paper defines such a standard, called the sequential data interchange standard, or SDIS. Both the SDIS data language and a parsing program for data that follow SDIS conventions are described. The parsing program will be made available to researchers who wish to develop analysis programs for sequential data