The addition of abscisic acid (ABA) to mature non-dormant seeds inhibits their germination. This effect of ABA might be related to its natural function as an endogenous inhibitor of precocious germination during seed formation. In this work, we studied how ABA affects the germination of mature seeds and the growth of nascent seedlings of Arabidopsis thaliana (L.) Heynh. Our findings were as follows: (i) inhibition by ABA was gradual, dose-dependent, and did not disappear after germination; (ii) inhibition of germination was relieved by the addition of metabolizable sugars or amino acids to the plating media; (iii) the effect of sugars and amino acids was cooperative, indicating that these two groups of metabolites relieve different deficiencies; (iv) ABA caused appreciable alterations in energy and nitrogen metabolism; and (v) ABA prevented the degradation of the seed storage proteins. In summary, ABA appears to inhibit seed germination by restricting the availability of energy and metabolites. This mechanism seems consistent with other known effects of ABA.