The integration of optical detection elements, such as waveguides and photodiodes, together with microfluidic channels on a single substrate is presented and discussed. The incorporation of such elements offers additional functionality, allows more compact designs and improves the potential for fabricating robust, reliable and efficient microanalytical devices for a number of biochemical and medical applications. However, high demands are set for the microfabrication and especially the simultaneous integration of several different functionalities is challenging. Different designs, their performances and possible applications for hybrid and monolithically integrated devices are sketched out.