Physiologically active substances contained in a biological sample not subjected to deproteinization can be converted to their derivatives at a high efficiency without being adversely affected by the protein present in the sample, and accordingly the analysis of said physiologically active substances in the form of said derivatives can be performed at a high precision.

Catecholamines in a living body fluid are analyzed by a process which involves reacting a living body fluid sample with a boron compound of the formula: ##STR1## wherein R is hydroxyl, aryl or alkyl, to form a complex of the boron compound with a catecholamine; deproteinizing the reaction solution containing the complex; decomposing the complex to release the catecholamine; labeling the released catecholamine to form a labeled catecholamine; eluting the labeled catecholamine adsorbed on a separation column; and detecting the eluted, labeled catecholamine. Advantageously, this process enables catecholamines to be measured with a high recovery ratio and high accuracy by forming the catecholamines into a complex with a boron compound.

Catecholamines can be detected with high sensitivity in a shortened time period, by introducing a sample containing catecholamines into an adsorption column packed with an adsorbent to adsorb catecholamines to the column, then introducing a reagent for derivatization to effect pre-column labeling and then analyzing the pre-column labeled catecholamines by means of high performance liquid chromatography. Connection of the adsorption column and a separation column of high performance liquid chromatography via a fluid path changeover valve enables to automated analysis of catecholamines.