An ideal Kd value would be low, as this would indicate a stronger binding affinity between the antibody and antigen. The majority of antibodies have Kd values in the micromolar (10^-6) to nanomolar (10^-7 to 10^-9) range. Very high-affinity antibodies are in the picomolar (10^-12) range. As Kd values increase, the affinity between the two molecules weakens. Thus, the antibodies may not bind strongly enough to the antigen to be functional. Researchers typically attempt to use low Kd values instead of higher values in order to achieve tight binding between molecules. This is especially important for drug development, as the potency of drugs increases when the Kd value is lower. This is because the concentration of the drug-target complex is more thermodynamically stable than it is with unbound drug and target.