Figure 1. Allium cepa root length grown for 96 hr in zidovudine (black line) or nevirapine (grey line).

Expressed as percentage of the unexposed control with value 34.6±2.7 mm (mean ± SE; n = 5 bulbs/group). The drug concentration giving half maximal root growth length (EC₅₀) for zidovudine (ZDV) was 65.0 µM, and for nevirapine (NVP) was 92.5 µM. At the 400, 800 and 1200 µM doses, roots from the NVP-exposed groups were significantly longer than those from the ZDV-exposed groups.