Is there an internal flag that is accessible to a user written function that specifies the type of dataset being used - eg cross section, time series, panel? If the panel command is issued for a time series dataset, it generates an error message saying (roughly) that the command is only valid for a panel dataset. I would like to be able to carry out the same test in a function so as to terminate the function in an informative manner rather than generating potentially confusing messages from internal commands. I thought about testing $unit but that generates its own message if the dataset is not a panel. One way of doing this would be to extend the current set of isxxx functions or to add an accessor $datatype which would return a number or string reflecting the type of dataset. Gordon