The use of cavity length control to obtain multiline emission from a hybrid CO2 laser has been investigated. We have obtained simultaneous laser oscillation on up to four lines in the P and R branches of the 10 µm band by operating the c.w. section above the lasing threshold. For sub-threshold operation of the c.w. section the hybrid laser emission is restricted to the stronger 10P lines. © 1990 Chapman and Hall Ltd.