Although lectins, in general, are not very toxic, there are some relationships between lectins and toxins. BEA-type toxins can be divided into two main parts. One shows sugar-binding activity responsible for targeting. Another part, which possesses different enzymatic activity, determines the toxicity. The lectins isolated from Trichosanthes kirilowii share some properties with BEA-type toxin, e.g. ricin. Some toxins can perforate cell membrane, forming an ion channel. A lectin from Pinellia turnata may belong to this kind of toxin. Several lectins were isolated from snake venom, sharing homologous amino acid sequences with other components in venom, while a receptor of well known toxin in venom, phospholipase A(2), contains lectin-like domain. In the venom of Trimeresurus stejnegeri exists a C-type animal lectin. The conclusion is that both lectins and toxins may be involved in the defense mechanism of organisms.