We investigated the electrical and optical properties of light emitting devices based on poly-p-phenylene-vinylene (PPV). At room temperature I-V-characteristics in the dark reveal a good diode behaviour with a maximum rectification ratio of 10(6). The threshold voltage for visible electroluminescence (EL) is device dependent and under best conditions we measure values as low as 2 V forward bias. At low temperatures the rectification ratio is considerably smaller and EL can be observed in both current directions. Impedance measurements show that at room temperature our diodes can be described within the Schottky barrier model as a serial circuit of resistive and capacitive components. Aging experiments point to a significant influence of air on the electrical properties and consequently on the lifetime of the devices.