Allium test has already been used to determine cytotoxicity of waste drilling fluids. In the present work the cytotoxicity of four pure chemicals (Defoamex, Idthin 400, Magco Thin and Slick Pipe) was investigated. Those chemicals are components of drilling fluids, therefore, they are usually constituents of oil and gas industry waste waters. The tested chemicals were prepared in 1:9 dilution and cytotoxic effects on root-tip meristem ofAllium ascalonicum were analysed after 24-, 48- and 72-hour-treatments. All samples showed cytotoxicity which was proved by cytogenetic parameters such as inhibition of mitotic activity and increase of mitotic abnormalities and chromosomal aberrations in comparison with the control. Almost all mitotic abnormalities induced by four chemicals tested were the result of disturbed spindle mechanisms accompanied with stickiness. Slick Pipe revealed the most prominent mitodepressive effect and induced a high number of abnormalities. It caused a significant decrease of mitotic activity and increase of mitotic abnormalities after all three treatment durations, while chemicals Defoamex and Magco Thin showed a significant decrease of mitotic activity only after 72-hour-treatment. Chemicals Defoamex, Idthin 400 and Magco Thin revealed a significant increase of mitotic abnormalities after 48- and 72-hour-treatments.