The interaction of tertiarybutylarsine (TBAs), triisobutylgallium (TiBGa) and trisdimethyl-aminoarsenic (TDMAAs) with the GaAs(001)-2x4 surface is studied by scanning tunneling microscope. No adsorbates were observed after TBAs exposure at room temperature. In the case of TiBGa and TDMAAs, adsorbates were observed on the As dimer rows. They were adsorbed randomly at low coverage and formed a 4x4 structure at a full monolayer. Weak interaction between molecules and the GaAs surface is expected because the 2x4 structure of the clean surface was kept under the adsorbates.