In this paper, we consider ANSI C program slicing using XML (Extensible Markup Language). Our goal is to build a flexible, useful and uniform data interchange format for CASE tools, which is a key issue to make it much easier to develop CASE tools such as program slicers. Although XML has a great potential for such data interchange formats, we first point out that there are still a lot of challenging problems to be solved. Then, as a first step to our goal, we introduce ACML (ANSI C Markup Language), which describes the syntactic structure and static semantics for ANSI C code. In our preliminary experiment, we had a good result; it took only 0.5 man-month to implement Weiser's slicer based on ACML, whereas it took about 2 man-months to implement an ANSI C parser and static semantics analyzer of XCI (Experimental C Interpreter).