The transient electroluminescence of monolayer and bilayer sexithiophene-based diodes has been measured. The delay time of the luminescence onset of the monolayer diode corresponds to a hole mobility of 5 x 10(-6) cm(2) V-1 s(-1) which is considerably lower than that obtained by field-effect measurements. This is interpreted in terms of strong transient trapping. The bilayer diode presents a twofold time-resolved response which is attributed to the different mobility of its constituent layers.