The concentrations and distributions of dissolved free amino acids (DFAA) were determined in 31 hydrothermal fluid samples from the Logatchev field at 15°N and several hydrothermal vent fields between 4° and 9°S on the Mid-Atlantic ridge, sampled during three research cruises. The samples are derived from black smoker fluids with varying degrees of dilution, with end-member temperatures between 350 and 407°C, as well as of diffuse fluids with temperatures around 10°C. Most of the samples, even the hottest ones, contain significant amounts of DFAA and, with an average of 143 nM, more than in the deep water of the open ocean (below 50 nM, Lee and Bada, 1977). The highest values are found in diffuse fluids and the lowest in the hot fluids, but there are also some high-T fluids with high, as well as diffuse fluids with low concentrations. There are two larger groups of samples, distinguished by two different amino acid (AA) patterns: Group 1 has low concentrations in general, but relatively high concentrations of aspartic acid and glutamic acid, whereas group 2 has high abundances of aspartic acid, glutamic acid, serine, glycine, and alanine. The samples of the two groups do not share any other similarities, with the exception of their DFAA pattern. Thus, it appears that neither factor, such as fluid type or degree of dilution, influences the DFAA pattern, nor is the pattern site-specific. The presence of elevated AA concentrations in hydrothermal fluids implies that they are available as a nutrient source to vent organisms and as potential complexing agents for metals, possibly influencing their bioavailability and solubility.