We studied the life history of the least brook lamprey, Okkelbergia aepyptera, and the American brook lamprey, Lampetra lamottenii, in Delaware. Observations of nest construction and spawning in O. aepyptera are presented. Mean number of eggs per female is 874. Larvae average 3.40 mm TL at hatching. Analysis of length-frequency data for ammocoetes indicates that the duration of the larval period is at least 5.4 years. Length-weight equation for ammocoetes is Log W = -5.24 -f- 2.73 Log L. Meristic data are presented. Mean number of eggs in L. lamnltcnii is 1691. Larvae average 2.60 mm TL at hatching. Ammocoete length-weight equation is Log W = -5.31 -f 2.76 Log L. Comparisons are made with northern populations.