We have searched for molecular absorption lines at millimeter wavelengths in eleven gravitational lens systems discovered in the JVAS/CLASS surveys of flat spectrum radio sources .
Spectra of only one source 1030+074 were obtained in the 3- , 2- and 1.3-millimeter band at the frequencies corresponding to common molecular transitions of CO and HCO ^ { + } as continuum emission was not found in any of the other sources .
We calculated upper limits to the column density in molecular absorption for 1030+074 , using an excitation temperature of 15 K , to be N _ { CO } < 6.3 \times 10 ^ { 13 } cm ^ { -2 } and N _ { HCO ^ { + } } < 1.3 \times 10 ^ { 11 } cm ^ { -2 } , equivalent to hydrogen column density of the order N _ { H } < 10 ^ { 18 } cm ^ { -2 } , assuming standard molecular abundances .
We also present the best upper limits of the continuum at the lower frequency for the other 10 gravitational lenses .