A series of eight alkyl bis(biguanide) analogues of alexidine, N,N''''-1,6-hexanediyl bis[N'-(2-ethylhexyl)imidodicarbonimidic diamide] (1), was prepared. Five of these analogues constituted a series isolipophilic with 1 but with varying bridge length between biguanide moieties. The compounds were evaluated in vitro for antibacterial and antiplaque properties against Streptococcus mutans, Actinomyces viscosus, and Actinomyces naesludii. One analogue, N N,''''-1,6-hexanediyl bis[N'(n-octyl)imidodicarbonimidic diamide], appeared to be more effective than either 1 or chlorhexidine against this spectrum of dental plaque forming microorganisms.