xlsread
only returns numeric data when only one output is specified. If the .xlsx file contains only text data, it will return empty. To remedy this, specify the outputs:
[fileName,dirName]=uigetfile('.xlsx');
[~,~,rawData] = xlsread(fullfile(dirName,fileName));
will return the entire contents of the sheet without MATLAB parsing the results and deciding what's text and what's numeric data.