<t>no i meant you called in ExcelDNA the rtd with XlCall.Excel(XlCall.xlfEvaluate, "RTD(...)"); its the exact same thing in XLL Excel4/12(xlfEvalute....); But i also wrote the Exceldna xll and RTD (C++/COM) separately.then when i wrote a pure xll i did it the same way calling the same RTD. both work...