Teat lesions affect the dairyman by interfering with the milking process or by increasing the likelihood of intramammary infection. Lesions where the skin is broken are frequently infected. The viral, chemical, environmental, and equipment-induced lesions that lead to ulceration, hemorrhage, and scabbing are all associated with increased intramammary infection; however, this association does not necessarily hold true with the less severe conditions. The dry and flakey skin seen with certain teat dips, lime, or sunburn, the common teat-end callous condition, and the mild, temporary congestion or edema sometimes seen after machine milking usually do not lead to increased intramammary infection. When investigating a problem of increased intramammary infection, other factors should be discussed with the dairyman before suggesting that these conditions are the cause of the problem. Before making a diagnosis of machine-induced lesions, the milking equipment should be carefully inspected and tested. Although the equipment can and frequently does cause lesions, it rarely does so if it is properly set or maintained. Maintenance of inflations, pulsators, vacuum regulators, and vacuum pumps will frequently reveal the source of the problem. In most cases, an equipment malfunction must be quite severe to result in teat injury. Many teat-lesion problems are seasonal in occurrence. The problem will frequently subside in the spring only to reoccur in mid fall. In the midwestern United States, most teat-lesion problems occur from November to April. When investigating a teat-lesion complaint, a large proportion of the herd should be examined.(ABSTRACT TRUNCATED AT 250 WORDS)