The gradient elution behaviour of ten peptide analogues encompassing the primary amino acid sequences adjacent to the serine-19 phosphorylation site of myosin light chain has been investigated using a 30-nm pore diameter n-butilsilica stationary phase and 0.1% trifluoroacetic acid-water-acetonitrile mobile phases. Quantitative expressions derived from linear solvent strength theory and general plate height theory have been used to assess the influence of gradient time and flow-rate on the relative retentions and bandwidths of these peptides. The retention behaviour of these peptide analogues was found to closely mirror the predictions of linear solvent strength gradient elution theory. Although the experimentally observed bandwidth changes over a conventional range of gradient conditions (i.e. tG = 30-60 min) also correlated with bandwidth changes predicted on the basis of plate theory derived for low molecular weight organic molecules, for very steep and very shallow gradients divergencies from theory were observed. The significance of these discrepancies is discussed in relation to the influence of amino acid sequence changes rather than composition of these peptide analogues. These data allow the importance of sequential effects on the chromatographic behaviour and in particular, the resolution optimisation of these closely related peptides to be evaluated.