The idea that tetracycline may have antifilarial properties was first proposed in 1960. Data were subsequently published on the effects of tetracycline on the development and reproduction ofBrugia pahangiin both the mosquito and mammalian hosts. These studies were apparently ignored until recently. In 1998, it was suggested that the antifilarial properties of tetracycline may derive from the presence of the bacterial endosymbiontWolbachiain fi‐larial worms. In view of this renewed interest, we would like to highlight an old study on the prophylactic activity of tetracycline against three filarial species. Although this work was performed at the begining of the seventies, and presented at a congress in 1973, it has never been published. This study showed that tetracycline had a prophylactic effect against infection of the mammalian host (the gerbilMeriones unguiculatus) withB. pahangiandLito‐mosoides sigmodontis. On the other hand, no significant prophylactic effect of the drug was observed againstAcanthocheilonema viteaein the same host. The new data on the distribution and phy‐logeny ofWolbachiaendosymbionts in filarial nematodes, showing thatA. viteaeis uninfected and thatB. pahangiandL. sigmodontisare infected, suggest that the activity of tetracycline on the latter two species is related to the presence ofWolbachia.