To claim isolation of HIV by this method one must show:

1. Firstly, that the culture cell-free fluids contain particles having morphological characteristics of retrovirus the principle of which are:

1. a diameter of 100-120nm
2. condensed inner cores
3. surfaces studded with spikes

2. When these fluids are banded in sucrose gradients the particles accumulate, that is, band, at the density of 1.16g/ml.

3. At that density there is nothing but retroviral-like particles.

Once this is proven, one proceeds to characterise the particle proteins and nucleic acids. If the particles are retrovirus, they should contain only RNA and not DNA, as well as an enzyme, reverse transcriptase, that copies RNA into DNA.