The isolation and viability in vitro of anagen secondary hair follicles of the Cashmere goat were studied. Isolated hair follicles were used to determine the effects on hair shaft elongation, of prolactin and melatonin, hormones considered to influence hair follicle growth and activity in vivo. Intact hair follicles were isolated from the dermal layer of the skin singly or in groups using watchmakers' forceps under a dissecting microscope. The isolated follicles were maintained floating in Williams E medium. The medium was supplemented with 1 of 6 concentrations of ovine prolactin (0, 50, 200, 400, 800 and 4000 micrograms/l) for the culture of hair follicles isolated during July and August, and with 1 of 5 concentrations of melatonin (0, 50, 150, 300, 600 ng/l) for the culture of hair follicles isolated during September and October. There was clear evidence of DNA synthesis, observed by autoradiography, in matrix cells of freshly isolated follicles incubated for 6 h in the presence of [methyl-3H]-thymidine. Similar measurements after 96 h of maintenance indicated a marked reduction in the incorporation of [methyl-3H]-thymidine in matrix cells of the follicles studied. Prolactin and melatonin were shown to have a stimulating effect on hair shaft elongation of secondary follicles during 24 h periods of measurement and cumulatively over 120 h. Maximum hair follicle growth was observed in follicles exposed to 400 micrograms/l of prolactin and follicles exposed to 300 ng/l of melatonin. The number of follicles remaining viable during each 24 h measuring period was not affected by prolactin, but was significantly reduced by melatonin treatment after 96 h of maintenance.(ABSTRACT TRUNCATED AT 250 WORDS)