The Tully-Fisher relation was investigated using 13 galaxy samples, spanning a large range in galaxy densities. Two 21 cm line-width parameters (Vmax and WRi) and two magnitude systems (BT0 and H-05c) were used. Two statistical tests were adopted to compare the Tully-Fisher relations of different samples. Many environments were considered, and a general homogeneity emerged, i.e., the Tully-Fisher relation showed no environment dependence. The comparison among samples with different data accuracy and/or different magnitude completeness appeared to be misleading. The two line-width parameters were found to be statistically equivalent, while the two magnitude systems gave different slopes to the relation. The blue and the infrared Tully-Fisher relations were found to give similar accuracies in the galaxy distance estimate.