Sulfoquinovosylacylglycerols (SQAGs), in particular compounds with C18 fatty acid(s) on the glycerol moiety, may be clinically promising antitumor and⁄or immunosuppressive agents. They were found originally as inhibitors of mammalian DNA polymerases. However, SQAGs can arrest cultured mammalian cells not only at S phase but also at M phase, suggesting they have several molecular targets.