1-naphthoxyacetic acid (1-NOA), 2-naphthoxyacetic acid (2-NOA), and 3-chloro-4-hydroxyphenylacetic acid (CHPAA) have been recently identified from a screen as inhibitors of auxin influx (Imhoff et al. 2000) and were found to phenocopy mutations in the AUX1 influx carrier (Perry et al. 2001). A recent, thorough analysis in the Zazimalová-lab in Prague (Lánkova et al. 2010) revealed that 1-NOA, although being most effective in blocking influx, also affects membrane cycling and thus also auxin efflux. Therefore, from the three inhibitors CHPAA seems to be the most specific. Working concentrations were 10-20 µM, whereby 10 µM were found to exert only mild long-term alterations of cell division and morphology.