The effect of tension of teatcup liners on teat end condition and quantity of keratin in the teat canal was investigated. Liner tension was increased by using longer teatcup shells. The first experiment used six Holstein cows in early lactation. Left quarters were milked with liners under medium or normal tension by using Conewango liners in 142 mm shells. Right quarters were milked with liners under high tension by mounting the liners in teatcup shells 149 mm in length. By day 16, teat end condition and sensitivity to manipulation were worsened by thrice daily milking when liners were under a higher tension. Two subsequent experiments each used 12 different Holstein cows. These cows were in mid lactation and were milked twice daily for 10 or 30 d. Left quarters were milked with liners under high tension. Right quarters were milked with liners under low tension by using teatcup shells 126 mm in length. The quantity of keratin removed during milking was not influenced by liner tension; however, the quantity of keratin at the end of the experiments was increased 10–20% in teats that were milked using liners under a higher tension. Histological analysis and keratin content were consistent with epithelial hyperplasia induced by milking with liners under increased tension.