An ethnobotanical study was conducted to find plants traditionally used against nuisance insects in three regions of Eritrea: highland, eastern escarpment and wet lowland. Six plants were collected, two of them were reported to be used against mosquitoes (Ocimum forskolei, Lamiaceae and Nicotiana glauca, Solanaceae), two others against fleas (Salvia shimperi, Lamiaceae and Otostegia integrifolia, Lamiaceae) and Neorautanenia mitis (Fabaceae) and Calpurnea aurea (Fabaceae) against animal lice. The effect of fresh leaves and shoots of O. forskolei hanging on walls at the head and foot of beds was tested in Eritrea against Anopheles arabiensis and 53% reduction in mean number of mosquitoes per house was achieved. Blood meals of mosquitoes collected from houses and pit shelters were analysed to determine whether biting diversion occurred due to the use of plants in the houses. No diversion of biting was observed to goats, which are abundant in the test area. Hot water distillates of N. glauca, S. schimperi and O. integrifolia were tested against An. gambiae s.s. in the laboratory using a Hemotek membrane blood feeder with pig skin replacing the parafilm membrane. The approximate doses in microl/cm(2) for 50% repellency with the extracts of S. schimperi, N. glauca and O. integrifolia were 0.97, 1.72 and 2.44, respectively. Even though the plants only achieved partial protection, they have a potential for widespread use as a complement to other control methods.