Technical Abstract: Phytotoxic microbial metabolites produced by certain phytopathogenic fungi and bacteria and a group of a phytotoxic plant metabolites including Amayllidaceae alkaloids and some derivatives of these compounds were evaluated for algicide, bactericide, insecticide, fungicide, and herbicide activities in order to discover natural compounds for potential use in the management and control of several important agricultural and household structural pests. Among the various compounds evaluated: 1) ophiobolin A was found to be the most promising for potential use as a selective algicide; 2) ungeremine was discovered to be bactericidal against certain species of fish pathogenic bacteria; 3) cycasin caused significant mortality in termites; 4) cavoxin, ophiobolin A, and sphaeropsidin A were most active towards species of plant pathogenic fungi; and 5) lycorine and some of its analogues (1-O-acetyl-lycorine and lycorine chlorohydrate) were very phytotoxic in the herbicide bioassay. Our results further demonstrate that plants and microbes can provide a diverse and natural source of compounds with potential use as pesticides.