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Context: The redshift of PG 1553+11, a bright BL Lac object (V~14), is stillunknown. It has been recently observed in the TeV band, a fact that offers anupper limit for the redshift z<0.4. Aims: We intend to provide a lower limitfor the distance of the object. Methods: We used a chi^2 procedure to constrainthe apparent magnitude of the host galaxy in archived HST images. Supposingthat the host galaxy is typical of BL Lac objects (M_{R} -22.8), a lower limitto the distance can be obtained from the limit on the apparent magnitude of thehost galaxy. Results: Using the 3 sigma limit on the host galaxy magnitude, theredshift is found to be greater or equal to 0.25. Conlusions: The redshift ofPG 1553+11 is probably in the range z=0.3-0.4, making this object the mostdistant extragalactic source so far detected in the TeV energies. We suggestthat other bright BL Lac objects of unknown redshift and similar spectroscopiccharacteristics may be interesting targets for TeV observations.

On the distance of PG 1553+11. A lineless BL Lac object active in the TeV band