Different types of gravitational lensing may affect GRBs if they lie at cosmological distances. Given the non-detection of lensing events due to the known galaxy field and assuming that QSO images are distorted by the same lens field, we have derived a very conservative upper limit on the redshift ofzgrbmax∼4.06.If dark matter comprises a certain fraction of the mass of the universe and is composed by individual objects, the lack of mega-, micro-, pico-, and femto-lensing events is also used to set limits on the cosmological abundance of these compact objects. ©1998 American Institute of Physics.