The antiviral lectins griffithsin (GRFT), cyanovirin-N (CV-N) and scytovirin (SVN), which inhibit several enveloped viruses including lentiviruses, were examined for their ability to inhibit entry mediated by Env proteins of delta- and gammaretroviruses. The glycoproteins from HTLV-1 were resistant to the antiviral effects of all three lectins. For gammaretroviruses, CV-N inhibited entry mediated by some but not all of the envelopes examined, whereas GRFT and SVN displayed only little or no effect.