Techniques for transmit power control for multiple antenna transmissions in an uplink are disclosed. A wireless transmit/receive unit (WTRU) generates at least one input stream for transmission and applies a gain factor to each channel. The gain factor is determined based on a reference channel power estimate. The WTRU generates at least two data streams from the input stream for transmission via a plurality of antennas and applies weights to the data streams. The gain factor and/or the weights are controlled such that a transmit power on each antenna is within a maximum allowed value. The WTRU may perform power scaling on a condition that a transmit power on any antenna exceeds the maximum allowed value. The WTRU may scale down an enhanced dedicated channel (E-DCH) dedicated physical data channel (E-DPDCH) first before other channels. For multiple E-DCH streams, the WTRU may calculate an E-DPDCH power offset based on an additional power offset factor due to multiple stream transmission.